, 


INTERNAL  COMBUSTION   ENGINES 


INTERNAL 
COMBUSTION    ENGINES 

/ 

THEIR    THEORY,   CONSTRUCTION 
AND    OPERATION 


BY 

ROLLA  C.  CARPENTER,  M.M.E.,  LL.D. 

AND 

H.  DIEDERICHS,  M.E. 

PROFESSORS  OF  EXPERIMENTAL  ENGINEERING,  STBLEY  COLLEGE, 
CORNELL  UNIVERSITY 


WITH  379  ILLUSTRATIONS 


SECOND   EDITION   REVISED 


NEW    YORK 

D.  VAN   NOSTRAND    COMPANY 

23  MURRAY  AND  i  9  o  9  27  WARREN  STS. 


Copyright,  1908,  by 
D.  VAN  NOSTRAND  Co. 


The  Plimpton  Press  Norwood  Mass.  U.SA. 


PREFACE 

THE  intention  of  the  authors  in  the  preparation  of  this  book 
has  been  to  present  in  as  simple  terms  as  possible  the  fundamental 
and  theoretical  principles  relating  to  the  internal  combustion 
engine,  and  to  describe  the  various  methods-  of  applying  these 
principles  to  practical  construction.  The  book  does  not  in  any 
way  treat  of  the  proportioning  and  the  strength  of  the  various 
machine  parts. 

The  general  treatment  of  the  subject  is  indicated  by  the 
various  chapter  headings.  Thus  the  first  five  chapters  relate  to 
definitions  and  theoretical  considerations,  the  subjects  being 
as  follows: 

CHAPTER      I.  DEFINITIONS  AND  CLASSIFICATION. 

CHAPTER     II.  THERMODYNAMIC  PRINCIPLES. 

CHAPTER  III.  THEORETICAL  DISCUSSION  OF  VARIOUS  CYCLES. 

CHAPTER   IV.  THEORETICAL  CYCLES  MODIFIED  BY  PRACTICE. 

CHAPTER     V.  THE  TEMPERATURE-ENTROPY  DIAGRAM. 

In  the  discussion  on  theoretical  cycles  in  Chapter  III,  very 
little  reference  has  been  made  to  cycles  not  in  actual  use.  The 
cycles  are  considered  principally  with  reference  to  their  practical 
application  and  any  danger  of  confusing  the  mind  of  the  student 
by  a  multiplicity  of  theoretical  cycles  of  no  practical  value  is 
avoided.  The  main  idea  of  Chapter  IV  is  to  show  how  the  lines 
of  the  real  cycles  differ  from  those  of  the  theoretical  cycles  laid 
down  in  the  previous  chapter,  and  to  discuss  briefly  the  reasons 
for  such  difference. 

The  five  chapters  following,  VI  to  X  inclusive,  take  up  the 
phenomena  of  combustion,  the  various  gas-engine  fuels,  and  the 
formation  and  properties  of  the  fuel  mixture.  Thus,  Chapter  VI 
treats  of  combustion  in  general  and  discusses  the  most  important 
properties  of  the  gases  usually  found  in  gas-engine  practice. 
Tables  are  given  embodying  the  important  constants  for  many  of 


179717 


vi  PREFACE 

these  gases,  and  the  chapter  ends  with  some  type  computations 
on  fuel  mixture  and  exhaust,  gas  constants  which  may  serve  as  a 
guide  for  similar  work  by  the  student. 

The  question  of  gas-engine  fuels  is  treated  in  the  next  three 
chapters  by  dividing  all  the  fuels  into  three  classes:  the  solid,  the 
liquid  and  the  gas  fuels.  Chapters  VII  and  VIII  take  up  the 
first  two  of  these  classes.  Broadly  speaking,  neither  class  of 
fuel  is  directly  available  for  gas-engine  work,  hence  it  was  thought 
desirable  to  show  in  these  chapters  also  the  means  by  which  these 
fuels  are  rendered  available.  Accordingly,  Chapter  VII  discusses 
producer  gas  and  describes  the  construction  and  operation  of 
the  most  important  types  of  producers,  while  Chapter  VIII  con- 
sists largely  of  a  description  of  the  various  vaporizing  devices 
used  for  crude  oil,  gasoline,  kerosene,  and  alcohol.  The  latter 
fuel,  recognizing  its  growing  importance,  has  been  treated  in 
some  detail.  Chapter  IX  relates  to  industrial  gases,  pointing 
out  briefly  the  method  of  their  manufacture  and  giving  the  most 
important  gas  constants. 

In  Chapter  X,  after  discussing  the  fuel  mixture  and  its  most 
important  properties,  an  attempt  has  been  made  to  collaborate 
the  most  important  experiments  on  the  variation  of  the  specific 
heat  of  the  fuel  gases  with  a  view  to  ascertaining  the  present 
state  of  our  knowledge  on  this  point. 

Chapter  XI  gives  a  brief  outline  of  the  historical  development 
of  the  gas  engine,  the  various  types  being  described  only  where 
they  are  of  importance  in  connection  with  the  development  of 
modern  forms.  This  is  followed  in  Chapter  XII  by  an  extended 
description  of  the  most  important  forms  of  internal  combustion 
engines  found  in  the  market  at  the  present  time.  The  aim  of 
this  chapter  has  been  not  only  to  show  how  the  various  manu- 
facturers have  solved  what  is  fundamentally  the  same  problem, 
but  also  to  familiarize  the  student,  by  means  of  a  large  number  of 
illustrations,  with  the  main  constructive  features  of  the  gas 
engines  at  the  disposal  of  the  man  requiring  power. 

Two  of  the  important  problems  connected  with  the  gas  engine 
are  the  questions  of  ignition  and  of  governing.  The  former  is 
taken  up  in  detail  in  Chapter  XIII.  This  chapter,  after  mention- 
ing briefly  other  methods  of  ignition,  concerns  itself  mainly  with 
ignition  by  electric  spark,  as  being  the  most  important  method 


PREFACE  vii 

used  to-day.  The  chapter  also  takes  up  briefly  two  other  gas- 
engine  auxiliaries:  mufflers  and  starting  apparatus. 

Chapter  XIV  treats  the  governing  problem  by  discussing  first 
the  principles  of  the  various  systems  of  governing  employed,  and 
afterward  shows  the  mechanical  details  of  the  governors  used. 
It  is  beyond  the  scope  of  this  book,  however,  to  treat  of  the  prin- 
ciples of  governor  design. 

Chapter  XIV  discusses  various  methods  in  use  for  determining 
the  necessary  cylinder  dimensions  of  a  gas  engine  to  develop  a 
certain  given  power,  or  conversely,  to  determine  the  probable 
power  for  a  given  engine.  The  most  reliable  of  these  methods 
appears  to  be  based  upon  the  necessary  charge  volume  for  the 
given  power.  This  method,  the  authors  believe,  was  originally 
due  to  Giildner,  and  was  adapted  from  that  author's  hand-book 
"  Entwerfen  und  Berechnen  der  Verbrennungsmotoren." 

For  the  determination  of  the  power  of  automobile  engines, 
two  additional  semi-empirical  formulae  are  given,  and  the  results 
of  the  computations  by  the  various  methods  are  compared  by 
means  of  a  type  example. 

The  remaining  three  chapters  of  the  book  treat  of  what  might 
be  called  the  economic  side  of  the  internal  combustion  engine. 

Chapter  XVI  takes  up  the  methods  used  in/ the  testing  of  gas 
engines.  The  rules  followed  in  this  country  will  be  of  course 
the  code  laid  down  by  the  American  Society  of  Mechanical  Engi- 
neers. The  Code  of  the  German  Society  of  Engineers,  however, 
is  appended,  because  it  gives  additional  information  upon  some 
of  the  points  involved  and  because  it  treats  in  greater  detail  of 
gas  producers. 

The  results  of  tests  on  engines  and  producers  are  discussed  in 
Chapter  XVII.  The  various  factors  affecting  economy  are  taken 
up  in  somewhat  greater  detail  than  has  been  done  in  any  of  the 
previous  chapters.  Tables  are  given  showing  the  results  of 
numerous  tests  and  these  should  prove  valuable  in  furnishing  a 
guide  as  to  what  may  be  expected  of  other  installations  in  the 
matter  of  fuel  economy. 

Finally,  while  Chapter  XVII  treats  only  of  the  question  of 
fuel  economy,  Chapter  XVIII  takes  up  the  entire  financial  problem 
relating  to  the  gas  engine.  It  shows  in  brief,  as  far  as  the  infor- 
mation is  available,  the  probable  capital  cost  of  the  installation, 


viii  PREFACE 

the  cost  of  erection,  the  operating  expenses,  etc.  It  is  shown 
most  strongly  that  the  question  of  fuel  cost  is  not  always  the  im- 
portant item  of  the  problem,  a  point  which  is  often  lost  sight  of  in 
discussions  regarding  the  comparative  merits  of  various  prime 
movers.  It  must  be  confessed  that  reliable  information  regard- 
ing some  of  the  factors  in  this  financial  problem  is  still  very  scarce, 
owing,  of  course,  directly  to  the  comparative  youth  of  the  gas 
engine.  It  should  also  be  pointed  out  that  many  so-called  com- 
parisons between  various  prime  movers,  as  between  steam  and 
gas,  are  often  based  upon  hypothetical  assumptions  that  _  fit  only 
the  particular  case  under  discussion,  and  any  generalization  of 
the  results  obtained  often  leads  to  serious  misrepresentation. 

The  book  is  of  course  largely  compiled  from  different  sources 
and  is  in  the  main  an  outgrowth  of  a  course  of  lectures  on  the 
internal  combustion  engine  delivered  to  students  of  Sibley  College 
for  the  past  three  years.  Acknowledgments  are  due  to  numerous 
writers  upon  the  subject  for  the  facts  and  statements  presented. 
The  acknowledgments  have  generally  been  made  in  the  body  of 
the  book,  but  the  authors  desire  to  extend  herewith  special 
acknowledgment  to  the  following  European  authorities:  Messrs. 
H.  Giildner,  Dugald  Clerk,  Bryan  Donkin,  and  Aime  Witz,  and  to 
Professor  C.  E.  Lucke  of  Columbia  University  and  Mr.  F.  E. 
Junge  of  New  York. 

Thanks  are  also  due  to  various  manufacturers  for  kindly  fur- 
nishing the  text  and  illustrations  of  Chapter  XII. 

ITHACA,  N.  Y., 
April  23,  1908. 


PREFACE   TO   THE    SECOND   EDITION 


IN  presenting  the  second  edition  of  this  book  'the  authors 
wish  to  express  their  obligation  to  all  those  who  kindly  aided  in 
pointing  out  errors,  and  especially  to  Professor  H.  P.  de  Schweinitz 
of  Lehigh  University,  for  a  thorough  revision  of  the  first  two 
chapters. 

February  1,  1909. 


TABLE  OF  CONTENTS 


CHAPTER  I 

INTRODUCTION,    DEFINITIONS    AND    CLASSIFICATION,    INDICATED    AND 
BRAKE  HORSE-POWER 

PAGE 

Mechanical  Work 1 

Heat  and  Temperature 3 

Thermometers  and  Pyrometers 6 

Specific  Heat 12 

Heat  Unit  and  Mechanical  Equivalent  of  Heat       .......  15 

Entropy 15 

Classification  of  Engines 17 

The  Steam  Engine         18 

Hot  Air  Engines 22 

Classification  of  Internal  Combustion  Engines 27 

The  Engine  Indicator         .                  32 

Indicated  and  Brake  Horse-power 38 

Forms  of  Indicator  Diagrams 40 


CHAPTER  II 

THERMODYNAMICS  OF  THE  GAS  ENGINE 

Characteristics  of  Perfect   Gases 45 

Relation  of  Heat  Transmission  to  Changes  of  Volume  and  Pressure     .  48 

Transformation  to  Different  States 51 

Work  of  Isothermal  and  Adiabatic  Expansion 53 

Relation  of  Heat  and  Entropy 54 

Second  Law  of  Thermodynamics 54 

Graphical  Relations 55 

Comparison  of  Theoretical  and  Actual  Heat  Engines 61 

CHAPTER  III 

THEORETICAL   COMPARISON    OF    VARIOUS   TYPES   OF   INTERNAL   COM- 
BUSTION ENGINES. 

« 

Theory  of  the  Constant  Volume,  Beau  de  Rochas  or  Otto  Cycle    ...       65 
Theory  of  the  Constant -Pressure  or  Bray  ton  Cycle,  the  Diesel  Cycle     .        69 

ix 


X  TABLE  OF  CONTENTS 

PAGE 

Comparison  of  Various  Cycles 73 

Conditions  affecting  the  Choice  of  Best  Cycle 79 

CHAPTER  IV 

THE    VARIOUS   EVENTS   OF  THE   CONSTANT-VOLUME   AND   CONSTANT- 
PRESSURE  CYCLE   AS  MODIFIED   BY   PRACTICAL  CONDITIONS 

The  Four-Stroke  or  Otto  Cycle 84 

The  Suction  Stroke 84 

The  Compression  Stroke                     .  • 87 

The  Combustion  Line,  Typical  Indicator  Diagrams 90 

The  Expansion  Line 97 

The  Exhaust  Stroke 100 

The  Two-Stroke  Cycle        .      .      .      .  ' 102 

The  Constant-Pressure  Cycle .      .  104 

CHAPTER   V 
THE  TEMPERATURE  ENTROPY  DIAGRAM  APPLIED  TO  THE  GAS  ENGINE 

General  Relations  Involved 107 

Mathematical  Construction  of  the  Entropy  Diagram 112 

Interpretation  of  the  Diagram 119 

Graphical  Method  of  Constructing  the  Entropy  Diagram 120 

CHAPTER   VI    * 
COMBUSTION 

Perfect  Gases 126 

Combining   Weights   and    Volumes,   Combustion,    Heating   Value,    Air 

Required,  etc 127 

Calorimeters 129 

Tables  of  Constants  and  Typical  Example  of  Gas  Computations     .      .  138 

CHAPTER   VII 
GAS-ENGINE  FUELS,  THE  SOLID  FUELS,  GAS  PRODUCERS 

The  Production  of  Air  Gas 147 

The  Production  of  Water  Gas 147 

The  Production  of  Producer  or  Power  Gas 149 

Gas  Producers  in  Practice 156 

Classification  of  Producers 158 

Description  of  Pressure  Producers 159 

Description  of  Suction  Producers 165 

Description  of  Combination  Producers 173 

Some  Producer  Details  175 


TABLE  OF  CONTENTS  xi 


CHAPTER   VIII 

THE  GAS-ENGINE  FUELS,  —  LIQUID  FUELS:  CARBURETERS  AND 
VAPORIZERS 

PAGE 
Crude  Oils  and  their  Distillates,  Gasoline,  Kerosene,  Alcohol        .      .      .      178 

Mixing  Devices  for  Liquid  Fuels 185 

Description  of  Various  Types  of  Vaporizers  and  Carburetars  for  Gaso- 
line, Kerosene,  Crude  Oil  and  Alcohol 186 

Conditions  required  for  Proper  Gasification  of  Alcohol 205 

CHAPTER   IX 
GAS-ENGINE  FUELS,  —  THE  GAS  FUELS 

Illuminating  Gas 206 

Oil  Gas 207 

Coke  Oven  Gas 208 

Blast  Furnace  Gas 209 

Aeetylene 211 

Water  Gas 212 

Natural  Gas 212 

Table  of  Constants  for  Above  Gases .213 

CHAPTER   X 
THE  FUEL  MIXTURE,  —  EXPLOSIBILITY,  PRESSURE  AND  TEMPERATURE 

Explosibility  and  Explosive  Ranges 215 

Pressure  and  Temperature  after  Combustion,   Experiments  of  Clerk, 

Langen,  etc 220 

Velocity  of  Flame  Propagation  and  Time  of  Explosion 227 

CHAPTER   XI 
THE  HISTORY  OF  THE  GAS  ENGINE 

Origin      . 232 

Period  of  Speculation  and  Invention 232 

Period  of  Development 239 

Period  of  Application        257 

CHAPTER   XII 
MODERN  TYPES  OF  INTERNAL  COMBUSTION  ENGINES 

General  Features  of  Design • 263 

Gas  Engines  : 

Small  and  Medium  Sized  Engines 265 

Large  .Gas  Engines 304 


xii  TABLE  OF  CONTENTS 

Liquid  Fuel  Engines :  PAGE 

Stationary  Gasoline  Engines 358 

Marine  Gasoline  Engines 361 

Automobile  Gasoline  Engines 372 

Oil  Engines 375 

Alcohol  Engines 390 

CHAPTER   XIII 

GAS  ENGINE  AUXILIARIES  —  IGNITION,  MUFFLERS  AND  STARTING 

APPARATUS 
Ignition: 

Ignition  by  Open  Flame .  392 

Ignition  by  Hot  Tube 394 

Ignition  by  Heat  of  Compression 396 

Ignition  by  Electric  Spark 397 

Make-and -Break  Ignition 397 

Jump  Spark  Ignition 401 

Timers 405 

Spark  Plugs 406 

Auxiliary  Spark  Gap 409 

Relative  Advantages  and  Disadvantages  of  the  two  Systems  of 

Electric  Ignition      ...'.. 410 

Sources  of  Current  . 410 

Chemical  Generators 410 

Primary  Cells 410 

Storage  Cells 411 

Mechanical  Generators 415 

Dynamos  and  Magnetos 416 

Methods  of  Connecting  up  Primary  and  Secondary  Batteries     .      .      .  420 

High -Tension  Distributors 423 

Mufflers 426 

Starting  Apparatus 428 

CHAPTER   XIV 
REGULATION  OF  INTERNAL  COMBUSTION  ENGINES 

General  Considerations 439 

Systems  of  Governing 441 

The  Hit-and-Miss 442 

Quality  Governing 444 

Quantity  Governing 446 

Combination  Systems 447 

Governing  by  Timing  of  Spark 449 

Governing  of  2-Cycle  Engines 449 

Mechanical  Details  of  Governors  . 450 

Pendulum  or  Inertia  Governors  for  Hit-and-Miss  Regulation     .      .  450 


TABLE  Of1  CONTENTS  xiii 

PAGE 

Mechanical  Centrifugal  Governors  for  Hit-and-Miss  Regulation  .      .      .  454 

Governors  for  Quality  Regulation 457 

Governors  for  Quantity  Regulation 460 

Governors  for  Combination  Systems 462 

Governing  Details  of  2-Cycle  Engines 467 

CHAPTER   XV 
THE  ESTIMATION  OF  POWER  OF  GAS  ENGINES 

Limits  of  Piston  Speeds  and  Rotative  Speeds 471 

Method  of  Determining  Power  by  Assuming  Mean  Effective  Pressure: 

Grover's  Formula 472 

Method  of  Determining  Power  by  Calculating  Mean  Effective  Pressure 

from  Tables  of  S.  A.  Moss 472 

Method  of  Determining  Power,  or  Cylinder  Dimensions,  by  Giildner's 

Method 477 

The  Power  Rating  of  Automobile  Engines 483 

CHAPTER    XVI 
METHODS  OF  TESTING  INTERNAL  COMBUSTION  ENGINES 

Rules  for  Conducting  Tests  of  Gas  and  Oil  Engines 486 

A.  S.  M.  E.  Code  of  1901 487 

Rules  for  Testing  Gas  Engines  and  Gas  Producers  Code  of  the  German 
Society  of  Engineers       . .511 

CHAPTER  XVII 
THE  PERFORMANCE  OF  GAS  ENGINES  AND  GAS  PRODUCERS 

The  Performance  of  Engines  as  affected  by: 

Cooling  Water  Conditions  and  Piston  Speed 530 

Compression 532 

Varying  Fuel  Mixture 533 

Point  of  Ignition 534 

Engine  Economy  Depending  upon  Load 537 

The  Heat  Balance ;      ...  539 

Results  of  Tests  on  Engines  and  Producers 542 

Table  of  Engine  Tests 544 

Table  of  Tests  of  Producers  and  Producer  Plants 546 

CHAPTER   XVIII 

COST  OF  INSTALLATION  AND  OF  OPERATION 

Cost  of  Producers  and  Engines 547 

Cost  of  Erection  548 


xiv  TABLE  OF  CONTENTS 

PAGE 

Piping  and  Auxiliaries 548 

Floor  Space  and  Buildings 549 

Cost  of  Operation 553 

Interest 553 

Depreciation 553 

Insurance 553 

Fuel  Costs 553 

Cost  of  Water  for  Cooling  and  Washing .      .  561 

Oil  and  Waste '.      .  564 

Attendance 565 

Maintenance  and  Repair 567 

Total    Operating  Costs,  and   Costs   as   Compared   with   other   Prime 

Movers  568 


CHAPTER  I 

INTRODUCTION,  DEFINITIONS,  CLASSIFICATION,  AND  FORM  OF 
INTERNAL  COMBUSTION  ENGINES,  INDICATED  AND  BRAKE 
HORSE-POWER 

i.  Mechanical  Work.  —  Work  is  done  when  resistance  is 
overcome;  it  is  measured  by  the  product  of  the  resisting  force 
and  the  distance  through  which  that  force  is  moved.  If  one 
pound  is  lifted  one  foot  high  in  opposition  to  the  force  of  gravity, 
a  quantity  of  work,  measured  by  the  product  of  one  pound  by 
one  foot,  is  performed,  which  quantity  is  known  as  a  foot-pound, 
and  is  the  unit  of  measurement  for  mechanical  work  in  countries 
where  the  pound  is  a  unit  of  weight  and  the  foot  a  unit  of  dis- 
tance. If  20  pounds  are  lifted  15  feet  the  work  performed  would 
be  similarly  20  X  15  foot-pounds  =  300  foot-pounds. 

In  countries  where  the  metric  system  is  used  mechanical 
work  is  measured  by  the  product  of  the  resisting  force  in  kilo- 
grams (2.2046  pounds)  multiplied  by  the  distance  in  meters 
(3.2808  feet);  the  product  is  expressed  in  kilogr ammeters  (7.233 
foot-pounds). 

The  foot-pound  or  kilogrammeter  is  a  gravity  measure  which 
depends  on  the  intensity  of  the  force  of  gravity  at  the  place, 
and  varies  with  that  force.  The  variation  is,  however,  so  slight 
for  different  positions  on  the  earth's  surface  that  for  all  practical 
engineering  work  no  sensible  error  is  produced  by  considering 
it  a  constant  quantity. 

The  unit  of  measurement  usually  employed  by  engineers  for 
expressing  the  rate  of  work,  or  the  quantity  of  work  done  in  a 
given  time  as  one  second  or  one  minute,  is  the  horse-power, 
which  has  been  arbitrarily  defined  as  equivalent  to  550  foot- 
pounds per  second  or  33,000  foot-pounds  per  minute.  This 
quantity  is  considerably  greater  than  the  power  a  horse  can 
exert,  at  least  for  any  considerable  length  of  time;  it  was  first 

1 


\>  INTERNAL  COMBUSTION   ENGINES 

used  by  James  Watt  in  defining  the  power  of  the  steam  engine 
and  has  been  established  by  long  use  as  a  definite  measure  of 
power.  In  France  the  term  Force  de  Cheval  is  applied  to  a  rate 
of  work  of  75  kilogrammeters  per  second  (542  J  ft.  Ibs.)  or  4500 
kilogrammeters  per  minute  (32549  ft.  Ibs.). 

In  general,  if  W  be  the  work  performed  against  the  pressure 
or  resisting  force  p  while  moving  through  the  space  or  volume  v, 

W  =  pv.  (1) 

Work  is  done  when  force  is  applied  so  as  to  produce  motion 
in  the  direction  of  action  of  the  force,  and  also  when  force  is 
employed  in  changing  the  velocity  of  a  body  already  in  motion. 
The  latter  condition  is  of  considerable  practical  importance  and 
can  be  considered  as  follows:  Suppose  a  body  whose  mass  is  M 
be  moving  in  a  certain  direction  with  a  velocity  u,  and  let  a  force 
exerting  a  momentum  P  be  applied  in  the  direction  of  motion, 
required  to  find  the  effect  produced  by  this  force  acting  through 
the  small  time  t,  during  which  the  body  moves  through  the  distance 
v,  and  has  at  the  end  of  the  time  the  velocity  u'. 

The  momentum  produced  by  the  force  in  one  unit  of  time  is 
P,  and  in  t  units  of  time  it  is  Pt.  Since  this  is  equal  to  the  increase 
of  momentum  produced,  we  have 

Pt  =  M  (u'  -  u). 

As  the  distance  is  equal  to  the  mean  velocity  multiplied  by  the 
time,  we  have 

v  =  %(u'  +  u)  t. 

By  multiplying  the  above  equations, 

Pvt  =  J  (Mu'2  -  Mu2)  t; 
dividing  by  t, 

Pv  =  i  (Mu'2  -  Mu2)  (2) 

.  Pv  is  the  mechanical  work  done  in  overcoming  a  resistance; 
the  expression  J  Mu2  is  the  kinetic  energy.  From  this  it  is  seen 
that  the  mechanical  work  done  is  measured  by  the  increase  in 
.the  kinetic  energy  produced. 

The  mechanical  work  done  by  a  fluid  during  a  change  of 
volume  from  v  to  vf  is  equal  to  the  mean  resistance  overcome,  or 


INTRODUCTION,  DEFINITIONS,  ETC.  3 

pressure  exerted,  p,  multiplied  by  the  change  of  volume.     That 
is,  in  general, 

W  =  fvpdv  (3) 

W  =  p(v'  -  v) 

In  the  operation  of  an  engine,  the  working  fluid  expands  and 
contracts  as  the  piston  moves  forward  and  backward,  and  in  one 
or  more  revolutions  returns  to  its  initial  condition,  so  far  as 
pressure,  volume  and  temperature  are  concerned,  and  then 
passes  through  the  same  stages  of  expansion  and  contraction  as 
before.  The  period  through  which  these  changes  take  place  is 
termed  a  cycle. 

The  work  performed  in  a  cycle  would  be  equal  to  the  mean 
pressure,  p,  exerted,  multiplied  by  the  total  volume,  vr,  swept 
through;  that  is 

W  -  =  pv'.  (4) 

Mechanical  work  can  be  represented  by  a  diagram  in  which 
the  pressure  exerted  or  resistance  overcome,  p,  is  represented  by 
the  ordinates,  and  the  volume  v  by  the  abscissa.  Such  a  diagram 
is  called  a  pressure-volume  diagram;  its  area  is  equal  to  fpdv, 

and  is  proportional  to  the  work  performed. 

Thus  in  Fig.  1-1,  if  the  distances  parallel  to  OY  represent 
the  pressure  at  any  given  point,  and  the  distances  parallel  to  OX 
the  corresponding  volume,  then  will  the  total  work  done  in  chang- 
ing from  the  highest  to  the  lowest  pressure  and  from  least  to 
greatest  volume  be  represented  by  the  area  of  the  figure  a  b  d  e  /. 

2.  Heat.  —  Heat    is  a    peculiar   form  of  energy;  it   may  be 
generated  by  the  application  of  mechanical  work,  the  amount  so 
produced  being  exactly  proportional  to  the  mechanical  energy 
which  disappears.     Conversely,   mechanical   work   may  be  done 
by  the  action  of  heat,  and  for  every  foot-pound  of  work  so  done 
a  definite  amount  of  heat  is  put  out  of  existence.     Heat  is  also 
produced   by  a  form  of  chemical  action  known  as  combustion, 
during  which  operation  fuels  are  burned. 

3.  Temperature.  —  The    temperature    of    a    body    is    defined 
by  Maxwell  *  as  "  its  thermal  state  with  reference  to  its  power  of 
communicating  heat  to  other  bodies." 

*  Theory  of  Heat. 


4  INTERNAL  COMBUSTION   ENGINES 

A  body  transmitting  heat  to  another  is  at  a  higher  tempera- 
ture and  is  said  to  be  hotter;  conversely,  one  receiving  heat  is  at 
a  lower  temperature  and  is  said  to  be  colder. 

Heat  flows  from  a  hotter  to  a  colder  body,  but  not  conversely, 


100 


-Ibs. 


01- 


0.0        0.1         0.2        0.3        O.I  cu.  ft. 

FIG.  1-1.- — Pressure-volume  or  Work  Diagram. 

and  the  rate  of  flow  increases  with  the  difference  of  temperature, 
although  probably  not  exactly  in  the  same  ratio.  The  difference 
of  temperature  thus  causes  a  flow  of  heat  in  a  manner  somewhat 
smiliar  to  that  caused  by  a  difference  of  pressure  in  the  case  of 
water.  , 

The  terms  hotter  and  colder  are  relative  ones  commonly  applied 
to  distinguish  substances  having  relatively  a  higher  or  lower 
temperature.  It  should  be  noted  that  temperature  is  that 
property  of  heat  which  refers  to  its  intensity  or  transmission 
power  also,  that  heat  energy  may  exist  at  different  tempera- 
tures, and,  furthermore,  in  one  condition  may  be  much  colder 
than  in  another. 


INTRODUCTION,  DEFINITIONS,  ETC. 


The  following  scales  of  temperatures  are  in  common  use  in 
which  the  temperatures,  of  freezing  and  boiling  water  under  a 
barometric  pressure  of  29.92  inches  are  taken  as  points  of 
reference. 

The  Centigrade  scale  was  introduced  by  Celsius,  professor  of 
astronomy  in  the  University  of  Upsala  about  1742;  in  it  the  freez- 
ing-point is  marked  0  degrees  and  called  zero,  and  the  boiling- 
point  is  marked  100  degrees.  The  simplicity  of  dividing  the 
distance  between  the  points  of  reference  into  100  parts  and  call- 
ing each  of  them  a  degree  has  caused  it  to  be  generally  adopted 
along  with  the  Metric  System  for  scientific  use,  especially  on  the 
Continent  of  Europe.  The  other  scales  are  called  by  the  names 
of  those  who  introduced  them. 

Fahrenheit  of  Dantzig,  about  1714,  introduced  a  thermometer 
scale  in  which  the  freezing-point  was  marked  32  degrees  and  the 
boiling-point  212  degrees,  the  space  between  the  reference  points 
being  divided  into  180  equal  parts  called  degrees,  and  the 
graduation  extended  above  and  below  the  points  of  reference. 
A  point  32  degrees  below  freezing  was  called  zero.  Despite  the 
inconvenience  of  the  scale  of  the  Fahrenheit  thermometer  it  is 
in  general  use  by  English-speaking  people  for  commercial  and 
business  purposes,  and  for  that  reason  will  be  used  principally  in 
this  treatise. 

Reaumur  introduced  a  thermometer  scale  about  1730  in 
which  the  freezing-point  is  marked  0  degrees  and  the  boiling- 
point  80  degrees,  which  is  used  to  some  extent  on  the  Continent  of 
Europe  for  medical  purposes. 

The  following  table  gives  the  comparative  value  of  the  three 
thermometric  scales: 

THERMOMETRIC  SCALES 


Fahrenhei  t 

Centigrade 

Reaumur 

Degrees  between  freezing  and  boiling  .  . 
Assumed  temperatures  at  freezing-point 

180 
32 

100 
0 

80 

0 

Assumed  temperatures  at  boiling-point 
Comparative  length  of  a  degree 

212 
1 

100 
1.80 

2.25 

Comparative  length  of  a  degree 

f 

1 

To  transform   into  absolute   tempera- 

ture add  

460° 

273° 

218° 

6  INTERNAL  COMBUSTION   ENGINES 

4.  Absolute  Temperature  is  an  expression  for  the  value 
of  temperature  measured  from  an  ideal  point  called  the  absolute 
zero,  which  is  assumed  to  be  the  lowest  possible  point  on  any 
scale  of  temperature.  The  position  of  the  absolute  zero  can  be 
calculated  by  the  law  of  expansion  of  a  perfect  gas,  which  is 
expressed  by  the  simple  equation 


in  which  p  =  the  pressure,  v  =  the  volume  of  a  given  mass  of 
gas,  T  =  the  absolute  temperature,  and  R  =  a  constant  which 
varies  only  with  the  different  kinds  of  gas.  This  equation  can 
be  considered  as  the  characteristic  equation  of  a  permanent  gas, 
from  which  T  can  be  computed  if  p,  v,  and  R  are  known,  which  is 
the  case  with  most  of  the  gases. 

It  is  evident  that  the  value  of  one  degree  of  absolute  tempera- 
ture can  be  taken  at  pleasure  as  equal  either  to  that  on  the  Cen- 
tigrade or  Fahrenheit  scale. 

The  exact  location  of  the  position  of  absolute  zero  is  some- 
what in  doubt  since  it  is  determined  by  the  relative  expansion 
of  air,  nitrogen,  or  hydrogen  under  a  constant  pressure;  these 
gases  are  not  perfect  gases  and  the  expansion  in  volume  per 
degree  of  increase  in  temperature  may  not  be  exactly  the  same 
as  for  a  gas  which  could  not  be  liquefied  for  any  conditions  of 
pressure  or  temperature.  Preston  in  his  work  on  the  Theory  of 
Heat  states  that  the  most  trustworthy  observations  indicate  that 
the  absolute  temperature  of  freezing  water  is  273.14  Centigrade, 
which  would  correspond  to  491.65  Fahrenheit.  It  is  sufficiently 
near  for  all  practical  purposes  to  consider  the  temperature  of 
freezing  water  on  the  absolute  scale  as  273  degrees  Centigrade  or 
492  degrees  Fahrenheit,  and  these  numbers  will  be  used  in  this 
treatise  in  reducing  to  the  absolute  scale. 

From  this  it  is  seen  that  to  reduce  to  the  absolute  scale  it  is 
necessary  to  add  to  .  the  temperature,  if  expressed  in  degrees, 
Fahrenheit  460,  or  if  in  degrees  Centigrade  273. 

5.  Thermometers.  —  Instruments  for  measuring  temperature 
are  called  Thermometers. 

The  expansion  of  a  gaseous,  liquid  or  solid  body  under  con- 


INTRODUCTION,   DEFINITIONS,  ETC. 


stant    pressure   is   almost,    if   not   exactly,  proportional   to   the 
increase  of  temperature,  estimated  from  absolute  zero. 

In  the  thermometer  in  common  use  the  tempera- 
ture is  measured  by  the  expansion  of  mercury,  con- 
fined in  a  glass  tube,  from  which  the  air  has  been 
exhausted.  Such  a  thermometer  is  quite  satisfactory 
within  the  range  of  temperature  through  which  mer- 
cury will  remain  liquid.  In  the  better  grades  of  mer- 
curial thermometers  the  graduations  are  cut  with 
extreme  care  directly  on  the  stem.  The  glass  is  care- 
fully selected  and  is  permitted  to  season  or  age  until 
molecular  changes  have  stopped  before 
graduation.  The  general  appearance  of 
such  thermometers  is  shown  in  Fig.  1-2. 
When  thermometers  are  likely  to  be 
used  in  temperatures  which  would  send 
the  mercury  column  above  the  limits  of 
the  graduations,  it  is  desirable  to  have 
an  extra  bulb,  called  a  safety-bulb,  at  the 
top,  to  prevent  breaking  from  overheat- 
ing. Mercurial  thermometers  can  be  used 
from  a  temperature  about  40  degrees 
below  zero  to  600  degrees  above  zero 
Fahrenheit.  By  filling  the  space  above 
the  mercury  with  some  neutral  gas  as 
N  or  CO2  under  pressure  the  upper  limit 
may  be  raised  some  hundred  degrees; 
but  as  the  melting-point  of  glass  is  low,  FlG-  1~2-  — 
the  upper  limit  can  scarcely  ever  exceed 
800  degrees  to  900  degrees  Fahrenheit. 
METALLIC  THERMOMETERS  in  which 
the  expansion  of  a  metal,  or  the  difference  in  expan- 
sion of  metals  of  two  different  kinds,  is  multiplied 


FIG.    1-3.  — 
Metallic 
Pyrometer. 


Mercurial 
Thermom- 
eter. 


by  a  system  of  levers  so  as  to  move  a  hand  over  a  dial  are  fre- 
quently used  for  the  measurement  of  temperature.  Such  ther- 
mometers are  sometimes  called  pyrometers.  An  illustration  of 
such  a  thermometer  is  shown  in  Fig.  1-3. 

The  metallic  thermometer  can  be  used  for  temperatures  not 
exceeding  1200  degrees  to  1500  degrees  Fahrenheit,  but  it  is  sel- 


8 


INTERNAL  COMBUSTION   ENGINES 


dom  an  instrument  of  accuracy  and  is  extremely  liable  to  acci- 
dent. The  scale  of  these  instruments  should  be  frequently  com- 
pared with  the  boiling-point,  and  adjusted  if  not  found  correct. 
It  has  already  been  shown  that  air  or  permanent  gases  like 
nitrogen  and  hydrogen  when  under  a  constant  pressure  will  ex- 
pand in  volume  in  proportion  to  the  absolute  temperature,  or 
when  confined  so  as  to  have  a  constant  volume  will  increase  in 
pressure  in  proportion  to  the  absolute  temperature. 

It  follows  from  this  that  if  air  be  maintained  at  a  constant 
volume  and  heated,  its  absolute  pressure  will  increase  with  the 
absolute  temperature,  or  vice  versa,  if  it  be  maintained  at  con- 
stant pressure,  its  volume  will  vary  with  absolute  temperature. 

The  air  thermometer  constructed  in  accordance  with  either 
principle  is  used  as  a  standard  way  of  measuring  temperature, 
but  because  of  the  extreme  difficulty  of  maintaining  constant 
pressures  or  constant  volumes  it  is  an  awkward  instrument  to 
use  and  is  employed  very  little  in  the  ordinary  measurement  of 
temperature.  The  Jolly  form  of  constant  volume  air  thermom- 
eter is  shown  in  Fig.  1-4.  The  leg 
C  F  has  a  flexible  connection  at  the 
bottom  and  may  be  raised  to  maintain 
a  constant  .volume  of  air  from  the  bulb 
L  to  the  line  A  B.  The  increase  of 
pressure  is  measured  by  a  scale  attached 
to  C  G. 

ELECTRICAL  THERMOMETERS.  — 
Temperature  may  be  measured  by  elec- 
trical thermometers,  of  which  there  are 
two  classes.  In  one  class  a  conducting 
circuit  is  formed  of  two  different  metals, 
such  a  construction  being  frequently 
termed  a  thermo- element,  a  number  of 
these  connected  together  is  known  as 

a  thermopile.  In  this  construction  an  electro-motive  force  is  pro- 
duced which  is  proportional  to  the  difference  of  temperature  of 
the  junctions  and  may  be  measured  by  a  sensitive  galvanometer. 
If  one  of  the  junctions  be  maintained  at  a  constant  or  known 
temperature,  the  temperature  of  the  other  may  be  computed 
from  the  reading  of  the  galvanometer.  For  the  measurement  of 


FIG.  1-4.  —  Jolly  Air  Ther- 
mometer. 


INTRODUCTION,  DEFINITIONS,  ETC. 


9 


high  temperature,  metals  having  a  high  melting-point,  such  as 
platinum  and  a  platinum-iridium  alloy,  may  be  used  for  the  ele- 
ments. 

The  LeChatelier  pyrometer  is  an   instrument  of  this   class; 


FIG.  1-5. — The  LeChatelier's  Electrical  Pyrometer. 

it  consists  of  a  galvanometer  connected  to  a  thermo- 
element B  as  shown  in  Fig.  1-5  and  is  extensively 
used;  the  thermo-element  is  constructed  of  plati- 
num and  platinum-rhodium  and  is  enclosed  in  a 
porcelain  tube,  as  shown  in  Fig.  1-6. 

The  Bristol  pyrometer  which  may  be  had  with  a 
recording  device  belongs  to  the  above  class. 

Another  class  of  electrical  thermometers  is  based  on  the  law 
of  increase  of  electric  resistance  of  metals  due  to  the  rise  of  tem- 
perature. With  this  class  of  thermometers  the  difference  in 
temperature  can  be  determined  from  the  measurement  of  the 
drop  in  potential  for  a  known  current  passing  through  a  coil. 
This  method  is  employed  in  the  platinum  thermometers  of  Sie- 
mens, Calendar,  and  various  others.  The  electrical  thermom- 
eters are  superior  to  all  others  for  many  uses. 

OPTICAL  PYROMETERS.  —  The  approximate  temperature  of  in- 
candescent bodies  may  be  determined  by  the  color  of  the  radiant 
rays.  Pouillet,  as  the  result  of  a  large  number  of  experiments, 
concluded  that  all  incandescent  bodies  have  a  definite  and  fixed 


10 


INTERNAL  COMBUSTION   ENGINES 


color  corresponding  to  each  temperature,  as  shown  in  the  follow- 
ing table: 


Color 

Temp.  C. 

Temp.  F. 

Faint  red 

525 

927 

Dark  red 

700 

1292 

Faint  cherry 

800 

1482 

Cherry 

900 

1652      ' 

Bright  cherry 

1000 

1932 

Dark  orange 

1160 

2120 

Bright  orange 
White  heat 

1200 
1300 

2192 
2372 

Bright  white 

1400 

2552 

Dazzling  white 

1500 

2732 

The  fixed  relation  between  color  and  temperature  is  due  to 
the  fact  that  the  color  of  an  incandescent  body  varies  with  the 
wave  length  which  is  a  function  of  the  tempera- 
ture.     A  number  of  optical   pyrometers   have 
been  devised  which  determine  the  temperature 
by  the  appearance  of  the  heated   body.     The 
Mesure  and  Noel  pyrometer  changes  the  wave 
lengths  by  the  rotation  of  the  plane  of  polariza- 
tion of  light  passing  through  a  quartz  plate  cut 
perpendicularly  to  its  axis.     In  the  use  of  the 
instrument    the    temperature   is    measured    by 
noting  the  angle  through  which  the  analyzer  is 
turned  in  order  to  produce  a  lemon  yellow  color. 
The  Morse  thermo-gage,  which  is  extensively 
used  in  the  steel  industry,  consists  of  an  incan- 
descent lamp  with  a  rheostat  arranged  so  that 
the  current  flowing  through  it   and   its   conse- 
quent brightness  may  be  regulated.     When  the 
FIG.    1-6.  —  The    ^m  of  the  incandescent  lamp  becomes  the  same 
Le  Chatelier    color  as  that  of  the  object  the  temperature  is 
Thermo-Ele-    computed  from  the  reading  of  a  milli- volt  meter 
arranged  to  measure  the  current.     The  tempera- 
ture corresponding  to  a  given  electrical  reading  is  determined  by 
calibration. 

The  optical  pyrometers  are  convenient  and  of  approximate 


INTRODUCTION,  DEFINITIONS,  ETC.  11 

accuracy  in  determining  high  temperatures  of  incandescent  bodies. 
They  are  of  no  value  in  determining  temperatures  of  combustible 
objects. 

VAPOR  THERMOMETERS.  --  The  pressure  produced  by  a  satu- 
rated vapor  confined  in  a  closed  vessel  increases  with  the  tem- 
perature, in  accordance  with  a  known  law  or  a  law  which  may 
be  determined.  By  providing  a  suitable  pressure  gage  and 
attaching  it  to  a  closed  vessel  of  the  proper  shape  the  tempera- 
ture may  be  obtained  from  the  pressure  readings,  the  value  of 
which  are  known,  or  from  the  dial  readings  of  the  pressure  gage, 
which  may  be  graduated  by  trial  into  degrees  of  temperature.  An 
instrument  of  this  type  is. made  by  Schaeffer  and  Budenberg  and 
called  by  them  a  Thalpotasimeter. 

CALOMETRIC  THERMOMETER.  —  The  temperature  can  also  be 
measured  by  calometric  methods,  by  heating  a  body  of  known 
weight  and  specific  heat  to  the  temperature  which  it  is  desired 
to  measure,  then  transferring  this  body  with  as  little  cooling  as 
possible  to  a  vessel  containing  a  known  weight  of  water. 

The  equation  for  this  operation  will  be  expressed  as  follows: 

W  (t  -O  =  ws  (tx  -  t), 

in  which  W  =  equivalent    weight    of   water   and    its   containing 

vessel. 

w  =  weight  of  heated  body, 
s  =  specific  heat  of  hot  body. 
f  =  original  temperature  of  water. 
t  =  final  temperature  of  water. 
tx  =  temperature  of  hot  body. 

A  ball  of  platinum,  copper,  porcelain,  or  burned  fire  clay  answers 
nicely  for  the  body  to  be  heated. 

FUSION  THERMOMETERS.  —  The  temperature  can  be  approxi- 
mately determined  from  the  known  melting-points  of  metallic 
bodies,  on  the  principle  that  the  temperature  will  be  higher 
than  the  melting-point  of  a  body  that  melts,  and  lower  than  the 
melting  temperature  of  one  that  does  not  melt.  In  place  of 
metallic  bodies  a  series  of  fusible  clay  cones  called  "  Seger  cones," 
whose  melting-points  are  known,  are  often  employed  in  the  same 
manner. 


12 


INTERNAL  COMBUSTION   ENGINES 


6.  Specific  Heat.  —  Different  materials  of  the  same  weights 
have  different  capacities  for  absorbing  heat  for  a  corresponding 
change  of  temperature;  thus  one  pound  of  water  will  absorb 
about  nine  times  as  much  heat  as  one  pound  of  wrought  iron  for 
the  same  change  of  temperature.  This  peculiar  heat  capacity 
of  bodies  compared  with  water  is  termed  specific  heat,  which  is 
usually  defined  as  follows: 

The  specific  heat  of  a  body  is  the  ratio  of  the  quantity  of  heat 
required  to  raise  that  body  one  degree  in  temperature,  to  the 
quantity  required  to  raise  an  equal  weight  of  water  at  standard 
temperature  one  degree. 

The  specific  heat  of  water  is  not  quite  constant,  being  nearly 
three  fourths  of  one  per  cent  higher  at  the  boiling  and  freezing 
temperatures  than  at  fifteen  degrees  Centigrade;  this  is  shown  by 
the  following  table  from  the  book  of  Steam  Tables  by  Professor 
Peabody : 

SPECIFIC  HEAT  OF  WATER 


Centigrade 

Fahrenheit 

Specific  Heat 

0°—  5° 

32°—  41° 

1.0072 

5  —10 

41  —50 

1.0044 

15  —20 

59  —68 

1.00 

20—25 

68  —  77 

0.9984 

25—30 

77  —86 

0.9948 

30  —35 

86—95 

0.9954 

40—45 

104  —113 

1.00 

45—155 

113—311 

1.008 

155—200 

311  —392 

1.046 

7.  Specific  Heat  of  a  Permanent  Gas.  —  In  general  the 
conditions  under  which  the  change  of  temperature  occurs  should 
be  distinctly  specified,  for  the  temperature  of  a  body  may  be 
varied  by  the  mechanical  work  done  in  the  compression  or  ex- 
pansion which  occurs.  The  change  of  volume  due  to  increase 
of  temperature  is  so  small  for  solids  and  liquids  that  the  external 
work  in  change  of  volume  may  be  neglected,  but  such  is  not  the 
case  for  gases.  For  this  reason  the  conditions  under  which  the 
heating  of  a  gas  takes  place  must  be  stated  when  referring  to  its 
specific  heat,  and  it  has  become  customary  to  speak  of  two  spe- 


INTRODUCTION,  DEFINITIONS,  ETC. 


13 


cific  heats  in  connection  with  any  gas,  namely,  the  specific  heat  at 
constant  volume,  and  the  specific  heat  under  constant  pressure. 
The  former  is  the  quantity  of  heat  required  to  raise  the  tempera- 
ture of  a  unit  mass  of  the  gas  one  degree  when  its  volume  is  kept 
constant,  and  the  latter  the  quantity  of  heat  required  to  raise  the 
temperature  of  a  unit  mass  one  degree  when  the  pressure  is  kept 
constant,  compared  with  that  of  a  unit  mass  of  water.  In  the 
first  case  the  pressure  increases  while  the  volume  is  kept  constant 
and  no  external  work  is  done;  in  the  latter  the  volume  increases 
under  constant  pressure,  and  an  amount  of  external  work  is  done 
which  is  measured  by  the  product  of  the  pressure  by  the  change 
of  volume. 

The  specific  heat  of  a  gas  at  constant  volume  bears  a  known 
relation  to  the  specific  heat  at  constant  pressure,  so  that  if  one 
be  determined  experimentally  the  other  may  be  computed.  It 
will  be  shown  later  that  the  specific  heat  at  constant  pressure 
equals  the  specific  heat  at  constant  volume  plus  a  constant  which 
depends  on  the  nature  of  the  gas.  That  is, 

Cp  =  Cv  +  R  when  expressed  in  heat  units,  and 
Kp  =  Kv  +  JR    when  expressed  in  foot-pounds. 

The  following  table  gives  the  specific  heats  of  constant  pres- 
sure and  volume  of  the  principal  gases : 

TABLE  OF  SPECIFIC  HEATS 


Gas 

e# 

Cv 

7 

Gas 

Cp 

Cv 

7 

H 
0 

N 

3.4090 
0.2175 
0.2438 

2.4177 
0.1543 
0.1729 

1.41 
1.41 
1.41 

CO 
CO2 
CH4 

0.2479 
0.2169 
0.5929 

0.1738 
0.157 

1.41 
1.29 

Air 
HsO(  vapor) 

0.2375 
0.4805 

0.1684 
0.3585 

1.41 
1.34 

C2H4 

0.4040 

0.320 

1.26 

In  the  above  table  Cp  =  Specific   heat   of   constant   pressure. 
Cv  =  Specific  heat  of  constant  volume. 
7  =  C-,  +  C., 

The  specific  heat  of  a  perfect  gas  is  considered  constant  by 
most  English  writers  who  discuss  the  subject.     Quite  a  number 


14  INTERNAL  COMBUSTION  ENGINES 

of  experiments  have  shown,  however,  that  it  varies  with  both  the 
pressure  and  the  temperature. 

In  the  French  work  by  A.  Witz  the  following  formula  is  given 
for  the  change  of  specific  heat  with  pressure: 

Cp  =  a  -f  b  (p  —  1),  in  which  a  and  b  are  constants  for  each 
gas  and  p  the  pressure  in  kilos  per  square  centimeter. 

The  specific  heat  of  all  vapors  which  are  liquefied  at  moderate 
temperature  undoubtedly  increases  with  the  increase  of  tempera- 
ture. This  subject  is  fully  discussed  in  Chapter  X  of  this  work. 

In  this  work  the  specific  heat  of  gases  will  be  considered  con- 
stant unless  otherwise  mentioned.  Any  error  caused  by  such 
consideration  will  not  usually  be  serious,  and  by  so  doing  the 
various  formulas  which  express  the  heat  capacities  under  actual 
working  conditions  are  much  simplified. 

The  specific  heat  of  a  mixture  of  various  gases  constituting 
a  known  weight  or  mass  is  equal  to  the  mean  specific  heat  of  the 
mixture,  and  is  found  by  multiplying  the  weight  of  each  component 
part  by  its  specific  heat  and  dividing  the  sum  of  the  products  by 
the  total  weight. 

8.  The  Heat  Unit.  —  Heat  is  measured  by  its  capacity  to 
raise  the  temperature  of  a  known  weight  of  water.  The  unit  of 
measurement  is  termed  a  calorie  in  the  metric  system,  and  a 
British  thermal  unit  (B.  T.  U.)  in  the  English  system.  A  calorie  is 
commonly  defined  as  the  heat  required  to  raise  one  kilogram  of 
water  from  the  freezing-point  to  one  degree  Centigrade,  and  a 
British  thermal  unit  (B.  T.  U)  that  required  to  raise  one  pound  of 
water  from  32  to  33  degrees  Fahrenheit.  Because  of  the  varia- 
tion in  the  specific  heat  of  water  near  the  freezing-point  Professor 
Peabody  in  his  Tables  of  Saturated  Steam  defines  the  thermal 
unit  as  that  required  to  raise  the  temperature  from  62  to  63  degrees 
Fahrenheit,  or  from  about  15  to  16  degrees  Centigrade. 

The  specific  heat  of  water  changes  slightly  for  different  tem- 
peratures as  already  noted,  but  it  can  be  considered  as  constant 
without  sensible  error  for  all  ordinary  purposes  in  the  measure- 
ment of  heat  when  the  temperature  is  maintained  between  the 
freezing  and  boiling  points. 

It  is  noted  from  the  above  statement  that  heat  is  measured 
not  by  the  temperature  alone  but  by  its  ability  to  heat  a  mass  of 
water  from  one  temperature  to  another ;  the  total  heat  expressed 


INTRODUCTION,   DEFINITIONS,  ETC.  15 

in  thermal  units  being  equal  to  the  product  of  the  weight  of  water 
by  the  change  of  temperature.  Thus  if  20  pounds  of  water  be 
heated  25  degrees  Fahrenheit,  the  heat  required  is  the  product 
of  20  times  25  =  500  B.  T.  U. 

9.  Mechanical     Equivalent     of     Heat.  —  The     mechanical 
equivalent  of  heat  is  the  amount  of  work  expressed  in  mechanical 
units  which  may  be  performed  by  the  transformation  of  one  heat 
unit  into  mechanical  work.     The  value  of  the  mechanical  equiva- 
lent of  heat  was  determined  experimentally  by  Joule  who  found 
that  772  foot-pounds  was  equivalent  to  one  B.  T.  U.  or  425.6  kilo- 
grammeters  to  one  calorie.     The  determinations  made  later  and 
with  more  accurate  instruments  by  Rowland,  reduced  to  the  sea 
level  and  to  45  degrees  of  latitude,  give  the  following  values  which 
are  now  generally  adopted: 

Expressed  in  calories,  J  =  426.9  kilogrammeters. 
Expressed  in  B.  T.  U.,  J  =  778    foot-pounds. 

In  this  work  J  is  used  as  the  symbol  for  the  mechanical 
equivalent  of  heat,  and  A  as  the  reciprocal  of  J.  That  is, 
J  =-  If  A. 

The  experiment  by  means  of  which  the  equivalent  value  of 
the  heat  unit  was  determined  in  units  of  mechanical  work  serve 
to  prove  the  general  mechanical  principle  of  the  conservation  of 
energy,  which  had  been  previously  stated  by  Clausius  as  follows: 
11  In  all  cases  where  work  is  produced  by  heat,  the  quantity  of  heat 
consumed  is  proportional  to  the  work  done;  and  conversely,  by  the 
expenditure  of  the  same  amount  of  work  the  same  quantity  of  heat 
may  be  produced.''  This  principle  is  often  called  the  first  law  of 
Thermodynamics. 

10.  Entropy.  —  One  of    the  qualities  or  properties  of  heat 
which  cannot  be  measured  by  any  simple  physical  apparatus  is 
termed  "Entropy."     This  same  quality  was  named  by  Rankine 
"the  Thermodynamic  Function";  its  value  is  such  that  its  change 
during   a   given    time   multiplied   by   the   absolute  temperature 
equals  the  total  heat  which  may  be  transformed  into  mechanical 
work.     From  this  definition  it  is  noted  that  the  product  of  abso- 
lute temperature  by  change  of  entropy   is   the  measure  of  the 
capacity  of  heat  for  performing  mechanical  work. 

As  an  illustration,  if  a  gaseous  body  under  pressure  be  allowed 


16  INTERNAL  COMBUSTION  ENGINES 

to  expand  without  receiving  or  giving  off  heat  its  entropy  would 
remain  constant  and  any  mechanical  work  performed  would  be 
done  at  the  expense  of  the  heat  existing  in  the  body.  A  change 
which  takes  place  without  gain  or  loss  of  heat  is  termed  adiabatic, 
which  condition  corresponds  to  that  of  constant  entropy. 

Expansion  or  compression  of  a  body  taking  place  without 
change  of  temperature  is  called  isothermal  expansion  or  compres- 
sion, and  lines  drawn  in  a  diagram  indicating  this  property  are 
termed  "  isothermal"  lines. 

Change  of  entropy  with  respect  to  heat  is  in  many  respects 
analogous  to  change  of  volume  in  respect  to  mechanical  work; 
it  has  already  been  shown  that  the  mechanical  work  is  equal  to 
the  change  in  volume  multiplied  by  the  resistance  or  pressure 
overcome.  If  we  denote  the  total  heat  capable  of  being  trans- 
formed into  mechanical  work  by  Q,  the  change  of  entropy  by  <f> 
and  the  absolute  temperature  by  T  ,  we  shall  have  the  following 

equations  :  ^  ,N 

W  —  (v  —  v)  p. 

Q   =  (*-  </>')  T. 

From  the  first  of  the  above  equations  it  is  noted  that  no 
mechanical  work  can  be  done  without  a  change  in  volume,  and 
further,  that  the  amount  of  work  done  is  measured  by  the  change 
of  volume  multiplied  by  the  pressure. 

From  the  second  it  is  seen  that  no  change  in  the  amount  of 
heat  which  a  body  contains  can  take  place  without  a  change 
in  entropy,  for  when  <j>  =  <£',  Q  =  0.  The  amount  of  heat 
transferred  is  measured  by  the  change  of  entropy  multiplied 
by  the  absolute  temperature. 

From  the  above 

,      W 

v  -v'  =  - 

p 

From  which  is  seen  that  the  change  in  volume  is  equal  to  the 
mechanical  work  performed  divided  by  the  mean  pressure. 


From  which  it  is  seen  that  the  change  in  entropy  is  equal  to 
the  total  heat  transformed  into  work  divided  by  the  absolute 
temperature. 


INTRODUCTION,  DEFINITIONS,  ETC.  17 

11.  Classification    of   Engines — The    action    of    an    engine 
is,  in  general,  to  produce  motion  against  a  resistance  or  to  per- 
form work.     Engines  are  popularly  classified  in  accordance  with 
the   nature   of  the   working   fluid,   as   hydraulic   engines,   steam 
engines,  gas  engines,  oil  engines,  etc.     They  may  be  more  scientifi- 
cally  classified   in  accordance   with  the  nature  of  the  working 
process  as  pressure  engines  and  heat  engines.     In  the  pressure 
engine  work  is  produced  by  change  of  pressure  without  change  of 
temperature,  as  illustrated  in  the  piston  water  engine.     In  the 
heat  engine  work  is  produced  by  transforming  heat  into  mechani- 
cal work,  which  process  is  accompanied  with  change  of  tempera- 
ture, and  usually,  also,  a  change  of  pressure. 

In  mechanical  structure  engines  are  of  two  classes,  recipro- 
cating and  rotary.  In  the  reciprocating  engine  a  piston  free  to 
move  in  a  cylinder  is  pushed  backward  and  forward  by  alternate 
changes  in  pressure  of  the  fluid  against  either  face.  The  recipro- 
cating motion  of  the  piston  is  converted  into  a  continuous  rotary 
motion  by  a  mechanism  usually  consisting  of  crank  and  fly-wheel 
which  will  be  described  later.  In  the  rotary  engine  a  rotary 
motion  is  directly  produced  by  the  force  due  to  pressure,  impulse, 
or  reaction  acting  upon  revolving  blades  or  pistons  arranged  in  a 
suitable  casing.  The  term  is  often  confined  to  a  structure  with 
a  revolving  piston  in  which  motion  is  produced  by  a  difference 
of  pressure,  whereas  the  term  turbine  is  applied  to  the  structure 
when  rotation  is  produced  by  impulse  or  reaction  of  the  jet.  In 
a  general  way  the  turbine  is  a  species  of  rotary  engine.  This 
treatise  will  be  principally  confined  to  internal  combustion  engines 
having  a  piston  with  reciprocating  motion. 

Engines  are  classified  as  single  acting  when  the  propelling 
force  is 'applied  to  one  side  of  the  piston  only,  &nd  as  double  acting 
when  it  is  applied  alternately  to  both  sides. 

Engines  are  classified  as  simple,  compound,  triple,  expansion, 
etc.,  depending  on  the  number  of  cylinders  through  which  the 
working  fluid  passes  in  succession  as  it  expands  from  highest  to 
lowest  pressure. 

12.  Classification  of  Heat  Engines.  —  Heat  available  for  use 
in  a  heat  engine  is  usually  produced  by  a  species  of  chemical 
action  termed   combustion.     Heat    engines  may  be   classified  in 
accordance  with  the  location  of  the  place  of  combustion  with 


18  INTERNAL  COMBUSTION  ENGINES 

respect  to  the  working  cylinder  as  external  combustion  engines 
and  internal  combustion  engines. 

The  external  combustion  engines  include  steam  and  other 
vapor  engines, hot  air  engines,  and  some  forms  of  gas  or  oil  engines; 
the  internal  combustion  engines  include  all  the  usual  forms  of 
gas  and  oil  engines  in  which  the  fuel  is  consumed  in  the  working 
cylinder.  In  this  work  the  term  gas  engine  will  be  frequently 
used  as  including  all  forms  of  internal  combustion  engines  adapted 
to  burn  gas  or  vapor  irrespective  of  the  nature  of  the  fuel. 

Of  these  various  types  of  engines  the  steam  and  the  gas 
engines  are  the  only  ones  of  practical  commercial  importance  at 
the  present  time.  The  hot  air  engine  was  built  extensively  about 
fifty  years  ago,  and  its  theory  was  thoroughly  investigated  at 
that  time.  It  failed  as  a  commercial  machine  because  of  the 
high  cost  of  repairs  and  operation;  it  is  principally  useful  at  the 
present  time  as  illustrating  the  practical  application  of  certain 
thermodynamical  principles. 

As  the  steam  engine  and  hot  air  engine  have  a  practical  bear- 
ing on  the  internal  combustion  engine,  a  short  description  is 
inserted. 

13.  The  Steam  Engine.  —  The  mechanism  of  the  steam 
engine  and  its  mode  of  operation  should  be  familiar  to  all  students 
of  the  internal  combustion  engine.  The  term  steam  engine  is 
used  here  in  its  broad  sense,  including  the  boiler, the  engine  proper, 
and  all  the  accessories  necessary  for  its  operation.  In  the  mode 
of  operation  of  the  steam  engine,  steam  is  produced  at  any  de- 
sired pressure  by  the  combustion  of  fuel  in  a  furnace  beneath  the 
boiler,  which  latter  is  a  strong  closed  vessel  containing  a  certain 
amount  of  water  and  into  which  water  is  introduced  by  a  feed 
pump  as  desired.  The  steam  engine  proper  is  pro  video!  with  a 
cylinder  in  which  is  fitted  a  piston  which  is  propelled  by  the 
steam  pressure  acting  on  one  or  both  sides.  The  admission  and 
discharge  of  the  steam  are  controlled  by  a  valve  or  valves  moved 
by  the  mechanism  of  the  engine,  the  form  of  which  varies  greatly 
with  different  types.  In  the  more  common  form,  a  slide  valve  is 
used  which  is  propelled  backward  and  forward  by  a  valve  rod 
moved  either  by  an  eccentric  or  by  a  short  crank  attached  to  the 
main  shaft.  The  valve  is  operated  so  as  to  admit  steam  at  nearly 
boiler  pressure  back  of  the  piston  for  a  portion  of  the  stroke,  and 


INTRODUCTION,  DEFINITIONS,  ETC.  19 

then  to  cut  off  communication  with  the  boiler,  after  which  the 
piston  is  pushed  forward  by  the  expansive  force  of  the  steam. 
The  valve  is  moved  at  the  end  of  the  stroke  so  as  to  open  com- 
munication between  the  cylinder  and  the  exhaust  pipe,  which  in 
the  case  of  a  non-condensing  engine  discharges  into  the  atmos- 
phere and  in  case  of  a  condensing  engine  discharges  into  a 
more  or  less  perfect  vacuum. 

The  motion  of  the  piston  is  communicated,  by  means  of  a 
piston  rod  which  slides  through  a  stuffing-box  at  the  end  of  the 
cylinder,  to  a  block  called  a  cross-head  which  moves  in  guides, 
from  which  motion  is  communicated  by  a  connecting  rod  to  the 
crank  of  the  main  shaft  so  as  to  produce  rotary  motion. 


S' 


FIG.  1-7.  —  Double  Acting  Steam  Engine. 

The  train  of. mechanism  of  the  ordinary  double-acting  steam 
engine  which  is  used  to  communicate  motion  from  the  piston  to 
the  ily-wheel  is  shown  in  Fig.  1-7,  in  which  P  represents  the 
piston,  p  the  piston  rod,  H  the  cross-head,  C  the  connecting  rod, 
M  E  the  crank,  E  the  crank  pin,  F  the  wrist  pin,  M  the  main  shaft, 
G  the  fly-wheel,  S  the  stuffing-box,  which  is  used  to  prevent 
leakage  of  steam  around  the  piston  rod.  The  cross-head  moves 
in  guides  K  which  direct  its  motion.  One  end  of  the  connect- 
ing rod  E  has  a  circular  motion,  the  other  a  rectilinear  motion. 
In  the  view  referred  to  the  valves  which  admit  steam  alternately 
to  the  ends  of  the  cylinder  are  not  shown. 

A  view  of  a  two-cylinder  single-acting  engine  is  shown  in 


20 


INTERNAL  COMBUSTION  ENGINES 


Fig.  1-8  in  section.  In  this  engine  the  steam  is  admitted  only  at 
one  end  of  the  cylinder  at  the  proper  intervals  of  time  by  the 
sliding  motion  of  the  piston  valve  V,  which  is  operated  by  the 


FIG.  1-8. — Two-cylinder  Single-acting  Steam  Engine. 

mechanism  of  the  engine  by  means  of  a  small  crank  attached  to 
the  main  shaft  and  the  various  link 'connections  shown. 

Steam  engines  are  frequently  built  compound,  in  which  case 
the  steam  works  in  succession  in  a  small  and  large  cylinder, 
termed  respectively  the  high-pressure  and  low-pressure  cylinder. 
These  cylinders  may  be  arranged  side  by  side  as  in  the  view  of  the 
single-acting  engine,  Fig.  1-8,  or  they  may  be  arranged  in  tandem 
as  shown  in  Fig.  1-9.  In  the  tandem  compound  engine  shown 


FIG.  1-9. — Tandem  Compound  Steam  Engine. 


INTRODUCTION,   DEFINITIONS,  ETC.  21 

the  supply  of  steam  is  admitted,  to  the  high-pressure  cylinder 
by  the  slide  valve  V  operated  from  the  small  crank  Ef ',  and  to  the 
low-pressure  cylinder  by  the  slide  valve  V  operated  from  the 
eccentric  E. 

Since  the  application  of  pressure  to  the  piston  as  described 
above  is  periodic  and  not  constant,  a  fly-wheel  consisting  of  a 
heavy  mass  of  metal  must  be  applied  as  shown,  to  produce 
uniform  motion.  To  regulate  the  speed  a  governor  is  used, 
which  is  constructed  so  that  the  variation  in  centrifugal  force 
either  tends  to  cut  off  the  supply  of  steam  or  to  close  the 
steam  valves  if  the  speed  become  higher  than  desired,  or  the 
reverse. 

An  indicator  or  pressure  volume  diagram  of  a  steam  engine  is 
shown  in  Fig.  1-35.  In  this  diagram  vertical  distances  are  pro- 
portional to  pressures  per  square  inch  acting  on  the  piston,  and 
horizontal  distances  to  the  space  passed  through  by  the  piston. 
The  diagram  shows  the  relation  of  pressure  and  volume  at  any 
point.  The  work  done  on  the  piston  is  proportional  to  the  area 
of  the  diagram. 

The  steam  engine,  as  will  be  shown  later,  does  not  realize  in 
the  work  performed  as  great  an  efficiency  on  the  basis  of  the  heat 
values  of  the  fuels  employed  as  the  gas  engine;  but  it  has  the 
advantage  of  being  adapted  for  the  burning  of  solid  fuels  under 
its  boiler  without  converting  the  same  into  gas,  and  this  in  a 
measure  sometimes  compensates  for  the  greater  heat  losses. 
The  steam  pressure  is  exerted  on  the  piston  for  a  much  larger 
portion  of  the  stroke  than  an  explosion  in  a  gas  engine  piston, 
and  as  a  consequence  the  inertia  of  moving  parts  is  depended 
upon  less  for  uniform  speed  than  in  the  gas  engine,  as  will  be 
afterwards  shown. 

In  the  past  the  steam  engine  has  had  a  great  advantage  over 
the  gas  engine,  due  to  the  fact  that  it  has  been  more  reliable  in 
operation  and  could  produce  a  more  nearly  uniform  motion. 
The  development  of  the  gas  engine  has,  however,  removed  in  a 
large  measure  such  defects,  and  at  the  present  time  there  is  no 
great  difference  in  respect  to  reliability  and  regulation  on  the 
part  of  these  two  classes  of  engines.  The  use  of  a  producer  in 
which  gas  can  readily  be  made,  from  solid  fuels  also  equalizes  any 
advantages  which  the  steam  engine  has  had  from  that  source. 


22 


INTERNAL  COMBUSTION  ENGINES 


14.  Hot  Air  Engines.  —  The  hot  air  engine  is  principally 
of  importance  to-day  for  its  scientific  value.  Its  actual  com- 
mercial use  is  confined  to  pumping  small  quantities  of  water 
under  favorable  conditions.  It  is  of  scientific  interest  because 
it  is  the  only  heat  engine  yet  produced  which  represents  almost 
perfectly  the  standard  ideal  cycle  of  Carnot,  with  which  the 
operation  of  nearly  all  heat  engines  is  compared. 

In  the  hot  air  engine  a  mass  of  air  is  successively  heated  and 
cooled;  during  the  time  that  it  is  heated  either  its  volume  or 
pressure  increases,  and  during  the  time  it  is  cooled  the  reverse 
operation  takes  place.     Mechanical   work   is  performed  by  the 
change  of  volume  or  pressure  which  is  utilized  for  moving  a  piston. 
The  principal  varieties  of  air  engines  may  be  classified  by  the 
following  distinctive  features:  1.  Change  of  temperature  at  con- 
stant pressure.     2.  Change  of  temperature  at  constant  volumes. 
3.  Heat  received  and  rejected  at  a  pair  of  constant  pressures. 
Ericsson's  engine,  best  known  as  the  caloric  engine,  may  be 

taken  as  an  example  of 
the  first  class.  In  this  en- 
gine, air  is  admitted  from 
the  atmosphere  to  the 
compressing  pump  at  the 
lowest  working  tempera- 
ture, and  compressed,  the 
temperature  being  main- 
tained constant  by  the 
action  of  some  refrigerat- 
ing apparatus.  The  air 
when  compressed  enters  a 
receiver.  It  is  then  ad- 
mitted to  the  working  cyl- 
||  inder,  being  heated  on  its 
passage  t6  the  higher  tem- 
perature, so  that  its  vol- 


FIG.  1-10.  —  Ericsson  Hot  Air  Engine. 


ume  is  increased  and  the  pressure  remains  constant  under  the 
movement  of  the  piston,  then  expands  with  its  temperature  main- 
tained constant  at  the  higher  limit,  and  is  finally  expelled  into 
the  atmosphere,  giving  up  its  heat*  to  the  regenerator,  to  be  used 
in  heating  the  volume  of  air  next  introduced. 


INTRODUCTION,  DEFINITIONS,  ETC.  23 

This  engine  is  represented  in  Fig.  1-10.  B  is  a  working  cylin- 
der, placed  over  the  furnace  H.  This  cylinder  consists  of  two 
parts;  the  upper  part  in  which  the  piston  works  is  accurately 
turned,  and  the  lower  part  in  which  the  air  receives  heat  from 
the  furnace  is  less  accurately  made.  A  is  the  piston  of  the  cylin- 
der, consisting  of  an  upper  part  which  is  accurately  fitted  and  pro- 
vided with  metallic  packings  so  as  to  work  air-tight  in  the  upper 
part  of  the  cylinder.  The  lower  part  is  somewhat  smaller  than 
the  cylinder,  is  hollow,  and  filled  with  brick  dust,  fragments  of 
fireclay,  or  some  slow  conductor  of  heat.  The  cover  of  the  cylin- 
der B  has  holes  in  it  marked  a  to  admit  the  external  air  to  the 
space  above  the  piston. 

D  is  the  compressing  pump  with  piston,  C,  which  is  connected 
to  the  piston  A  by  three  or  four  piston  rods,  of  which  two  are 
shown  at  d  d.  The  space  between  the  piston  C  and  A  is  open  to 
the  external  air.  In  operation  the  air  is  drawn  into  the  compress- 
ing pump  through  the  valve  c,  and  is  forced  out  after  being  com- 
pressed through  the  valve  e  into  a  receiver  marked  F.  It  is 
admitted  at  proper  intervals  of  time  by  the  valve  6  into  the 
working  cylinder  B,  being  heated  in  its  passage  by  hot  plates 
in  the  vessel  G,  termed  the  regenerator. 

It  is  further  heated  while  in  the  working  cylinder  by  the  heat 
from  the  furnace  ///the  effect  of  which  is  to  increase  the  tem- 
perature and  volume  underneath  the  piston.  The  increase  of 
volume  drives  the  piston  to  the  end  of  its  stroke.  The  exhaust 
valve  /  is  opened  by  a  mechanism  connected  to  the  engine  and 
the  working  gases  are  forced  outward  through  the  regenerator, 
G,  and  discharge  into  the  atmosphere  through  the  pipe  g.  The 
regenerator  is  a  vessel  nearly  filled  with  metallic  plates  which 
are  heated  by  the  escaping  gases  and  give  up  heat  to  the  engine 
gases,  thus  reducing  in  large  measure  the  heat  wastes  from  the 
engine. 

In  some  forms  of  the  Ericsson  engine  the  air  entering  the  com- 
pressor through  the  valve  c  is  taken  from  the  exhaust  opening 
g;  with  this  arrangement  the  same  mass  of  air  is  repeatedly  warmed 
and  cooled,  the  changes  of  temperature  taking  place  at  constant 
pressures. 

Ericsson's  caloric  engine  was  employed  to  drive  a  ship  across 
the  Alantic  in  1853.  The  ship  was  250  ft.  long,  had  paddle 


24 


INTERNAL  COMBUSTION  ENGINES 


wheels  32  ft.  in  diameter.  On  its  first  trial  trip  the  ship  made 
twelve  knots  an  hour  with  the  wind,  burning  six  tons  of  fuel  per 
day.  On  the  second  trial  the  maximum  speed  was  nine  knots. 
After  this  unfavorable  circumstances  came  to  light  and  in  1855 
the  engine  was  taken  out  and  a  steam  engine  substituted. 

Extended  accounts  of  the  Ericsson  and  other  hot-air  engines 
will  be  found  in  Knight's  Mechanical  Dictionary,  1873,  in  Apple- 
ton's  Cyclopedia  of  Mechanics,  1878,  in  Bourne's  work  on  the 
Steam,  Hot  Air,  and  Gas  Engine,  and  in  Rankine's  Steam 
Engine. 

Figure  1-11  represents  the  reciprocating  parts  of  an  air  engine 
of  the  class  in  which  temperature  is  changed  at  constant  volume. 
Such  an  engine  was  designed  and  built  by  Dr.  Robert  Stirling 
about  1850,  but  improved  by  various  other  inventors,  and  is  still 
built  and  sold  for  pumping  small  quantities  of  water  as  redesigned 
by  Rider. 

In  the  figure  D  C  A  B  is  the  air  receiver  or  heating  and  cooling 
vessel,  which  is  provided  with  a  furnace  underneath,  not  shown 
in  the  diagram;  G  is  the  working  cylinder  with  the  working 
piston  H.  The  receiver  and  cylinder  communicate  freely 

through  the  passage  F,  which  is  open  at 
all  times  when  the  engine  is  working. 
Within  the  receiver  is  an  inner  receiver 
or  lining  of  a  similar  figure,  which  has 
its  bottom  pierced  with  many  small  holes 
shown  with  dotted  lines  in  the  cut.  The 
annular  space  between  the  receiver  and 
its  lining  extending  along  the  side  of  the 
receiver  contains  the  regenerator,  which 
consists  of  a  series  of  oblong  strips  of 
metal  with  narrow  passages  between 
FIG.  1-11.—  Stirling  Hot  them.  The  inner  surface  of  the  cylindri- 
cal part  of  the  lining  from  A  A  to  C  C  is 

turned  and  the  plunger  E  is  fitted  nicely  in  this  portion.  The 
upper  portion  of  the  receiver  D  D  is  supplied  with  a  horizon- 
tal coil  of  fine  copper  tube,  through  which  a  current  of  cold 
water  is  forced  or  it  is  jacketed  with  cold  water,  and  is  termed 
the  refrigerator.  It  is  thus  noted  that  the  bottom  of  the  receiver 
is  kept  hot  while  the  top  is  kept  cold.  The  plunger  E  is  con- 


INTRODUCTION,   DEFINITIONS,   ETC. 


25 


nected  to  the  working  mechanism  of  the  engine  so  as  to  transfer 
a  certain  mass  of  air,  which  may  be  called  the  working  air,  from 
the  hot  to  the  cold  end  of  the  receiver,  and  in  so  doing  making  it 
pass  up  and  down  through  the  regenerator.  The  mechanism  for 
moving  the  plunger  E  is  so  adjusted  that  the  up-stroke  of  that 
plunger  takes  place  when  the  piston,  H ,  is  at  or  near  the  beginning 
of  its  forward  stroke,  and  the  down  stroke  of  the  plunger  when 
the  piston  H  is  at  or  near  the  beginning  of  the  back  stroke. 

An  air  engine  of  class  3,  which  received  and  rejected  heat  at 
constant  pressures,  was  designed  by  Jewell,  but  probably  was 
never  put  into  practical  use. 

HOT  AIR  ENGINES  OPERATED  BY  PRODUCTS  OF  COMBUSTION.  — 
Another  form  of  air  engine, 
which  Rankine  in  his  Steam 
Engine  terms  a  furnace  gas  en- 
gine, was  first  designed  by 
Cayley  of  England  and  Barre 
of  France,  and  was  redesigned 
and  improved  and  put  on  the 
market  in  this  country  about 
1865  by  Wilcox. 

The  engines  of  this  class 
operate  similar  to  a  steam 
engine,  pressure  being  pro- 
duced by  combustion  in  a 
closed  furnace  instead  of  in  a 
steam  boiler. 

In  the   operation   of    this 


FIG.  1-12.  —  Wilcox  Hot  Air  Engine. 


engine  (see  Fig.  1-12)  a  pump  draws  air  from  the  atmosphere 
through  valve  F,  compresses  it,  and  forces  it  into  a  strong  air- 
tight furnace  C  through  pipe  H ,  where  its  oxygen  combines  with 
the  fuel;  then  the  hot  gas  produced  by  the  combustion  mixed 
with  air  is  admitted  into  the  working  cylinder  through  pipe  B 
and  valve  7,  under  pressure  produced  by  the  temperature  of  com- 
bustion, where  it  drives  the  piston  P  through  part  of  its  stroke 
at  full  pressure  and  through  the  remainder  by  expansion,  until  it 
falls  to  atmospheric  pressure.  It  is  discharged  through  an  ex- 
haust valve  not  shown  and  a  pipe  X.  The  entering  air  is  heated 
by  a  regenerator  which  is  warmed  by  the  exhaust  gases.  In  the 


26  INTERNAL  COMBUSTION  ENGINES 

form  shown  (U.  S.  patent  May  19,  1865)  the  furnace  is  fed  with 
coal  through  a  double  valve,  which  is  so  constructed  that  it  can 
be  introduced  without  permitting  the  escape  of  more  than  a  very 
small  quantity  of  the  compressed  air.  In  the  Wilcox  engine, 
patented  Sept.  19,  1865,  the  furnace  was  fed  with  petroleum  oil 
under  pressure. 

Respecting  Cayley's  engine,  Rankine  states:  "The  cylinder, 
piston,  and  valves  of  this  engine  were  found  to  be  so  rapidly 
destroyed  by  the  intense  heat  and  the  dust  from  the  fuel  that  no 
attempt  was  made  to  bring  it  into  general  practical  use."  Wil- 
cox's  engine  never  met  with  commercial  success. 

Most  forms  of  the  gas  turbine  belong  to  a  class,  in  which 
pressure  is  produced  by  the  heat  of  combustion  of  the  gases  be- 
fore entering  the  turbine,  either  in  a  closed  combustion  chamber 
or  in  the  inlet  pipe.  As  the  supply  to  a  turbine  is  continuous 
no  inlet  or  exhaust  valves  are  required,  and  hence  the  trouble 
experienced  in  the  early  forms  of  this  engine  is  greatly  reduced. 

15.  Structure  and  Mode  of  Operation  of  the  Gas  En- 
gine. —  The  mechanism  of  the  ordinary  gas  engine,  using  the 
term  in  its  general  sense  as  covering  all  internal  combustion 
engines,  is  similar  in  most  respects  to  that  of  the  steam  engine, 
which  has  already  been  briefly  described.  It  consists  of  a  cylinder 
containing  a  piston  which  is  moved  by  the  pressure  produced  by 
the  explosion  of  a  charge  consisting  of  a  mixture  of  gas  or  vapor 
and  air  in  the  cylinder.  The  motion  of  the  piston  is  communi- 
cated to  a  main  shaft  by  a  connecting  rod  similar  to  that  used  in 
the  steam  engine.  The  valve  mechanism  of  the  gas  engine  serves 
to  admit  and  discharge  the  charge  at  the  proper  interval  of  time 
and  is  operated  by  the  mechanism  of  the  engine.  In  the  early 
development  of  the  gas  engine  a  slide  valve  was  used  to  a  con- 
siderable extent,  but  at  the  present  time  the  poppet  valve  is 
commonly  used  as  it  has  been  found  to  withstand  high  tempera- 
ture better  than  the  other  form. 

In  order  to  start  the  gas  engine  some  external  force  must  be 
provided  to  introduce  the  combustible  charge  into  the  working 
cylinder  and  give  it  the  initial  compression.  This  may  be  done 
in  the  first  instance  by  revolving  the  engine  by  extraneous  power, 
which  puts  the  piston  in  motion  and  serves  to  draw  in  the  neces- 
sary gas  and  air  by  suction  and  to  compress  the  same.  After  the 


INTRODUCTION,  DEFINITIONS,  ETC.  27 

engine  is  in  operation  the  inertia  of  the  moving  parts  keeps  it  in 
motion  and  serves  to  draw  in  and  compress  the  charge. 

It  is  quite  evident  that  the  amount  of  work  performed  will  be 
proportional  to  the  mass  or  weight  of  the  charge.  For  this 
reason  it  is  desirable  that  the  charge  be  under  as  much  com- 
pression as  practicable  at  the  time  of  ignition,  and  all  modern 
internal  combustion  engines  provide  means  for  compressing  the 
charge  previous  to  ignition  either  outside  or  inside  of  the  work- 
ing cylinder.  In  nearly  every  case,  in  the  modern  engine,  the 
compression  is  completed  in  the  working  cylinder. 

The  principal  events  in  the  operation  of  an  internal  combus- 
tion engine  are  as  follows: 

1.  Charging  or  suction,    during    which    time    the    charge    is 
drawn  into  the  cylinder. 

2.  Compression,  during  which  time  the  charge  is  compressed. 

3.  Ignition,  explosion,  and  expansion,  during  which  time  heat 
is  supplied  which  causes  the  combustion  or  explosion  followed  by 
the  expansion  due  to  increase  of  volume  caused  by  motion  of  the 
piston.     Ignition  may  take  place  under  conditions  of  (1)  constant 
volume,  (2)  constant  pressure,  or  (3)    constant  temperature. 

4.  Exhaust,  during  which  time  the  products  of  combustion 
leave  the  cylinder. 

16.  Classification  of  Internal  Combustion  Engines.  —  Gas 
engines  are  scientifically  classified  in  accordance  with  the  mode 
of  applying  heat  during  ignition  as  follows: 

1.  Engines  receiving  heat  with  charge  at  constant  volume; 
these  will  be  called  in  this  work  Explosion  Engines. 

2.  Engines  receiving  heat  with  charge  at  constant  pressure; 
these  will  be  called  in  this  work  Pressure  Engines. 

3.  Engines  receiving  heat  with  charge  at  constant  tempera- 
ture; these  will   be   called   in  this  work  Constant  Temperature 
Engines. 

In  the  first  of  the  above  classes  of  engines  the  charge  may  be 
ignited  with  or  without  previous  compression;  consequently  this 
class  may  be  subdivided  into  non-compression  and  compression 
engines,  the  non-compression  engine  has  entirely  gone  out  .of 
use  because  of  its  low  efficiency  and  small  capacity  for  a  given 
size.  Engines  of  any  class  may  be  either  two  or  four  stroke  cycle 
engines  as  explained. 


28  INTERNAL  COMBUSTION   ENGINES 

This  classification  is  based  on  the  characteristic  equation  ex- 
pressing the  relation  between  pressure,  volume,  and  temperature 
of  a  given  weight  of  a  perfect  gas,  which,  as  will  be  shown  later,  is 

P» 
T"=R 

in  which     p  =  absolute  pressure. 
v   =  the  volume. 
T  =  absolute  temperature. 
R  =  a  constant  for  any  given  gas. 

It  is  evident  that  the  heat  may  be  received  while  any  of  the 
variables,  pressure,  volume,  and  temperature,  remains  constant, 
that  is,  at  constant  volume  as  in  Class  1,  constant  pressure  as  in 
Class  2,  or  constant  temperature  as  in  Class  3. 

Internal  combustion  engines  are  often  unscientifically  classi- 
fied by  the  nature  of  the  working  fluid  as  gas  engines,  petrol 
engines,  and  oil  engines.  This  classification  gives  no  considera- 
tion to  the  fact  that  any  of  the  above  classes  will  operate  with 
any  of  the  fuels  named.  The  term  gas  engine  is  frequently  used 
in  this  work  in  its  general  sense,  as  applying  to  any  form  of  in- 
ternal combustion  engine. 

ENGINES  IGNITING  AT  CONSTANT  VOLUME,  OR  EXPLOSION 
ENGINES.  —  In  these  engines,  which  are  the  ones  commonly  used, 
the  various  operations  are  performed  in  the  order  mentioned 
above  in  each  working  cycle  of  the  engine.  These  engines  may 
be  divided  into  two  classes  accordingly  as  they  perform  these 
operations,  in  one  end  of  the  cylinder,  (a)  in  four  strokes  or  (6) 
in  two  strokes. 

In  this  class  of  engines  the  combustion  is  practically  in- 
stantaneous and  of  the  nature  of  an  explosion,  taking  place  under 
normal  conditions  while  the  volume  of  gas  remains  constant, 
thus  producing  an  extremely  rapid  rise  of  pressure. 

(a)  Four-Stroke  Cycle  Engine.  —  The  internal  combustion 
engine  most  commonly  used  ignites  the  charge  while  its  volume 
remains  stationary,  and  requires  four  strokes  for  one  cycle  of 
operation.  For  this  reason  it  is  known  as  the  jour-stroke  cycle  or 
four-cycle  engine.  This  engine  as  ordinarily  built  is  a  single- 
acting  engine  with  all  the  operations  performed  on  one  side  of 


INTRODUCTION,  DEFINITIONS,  ETC. 


the  working  piston.  A  diagram  showing  its  general  construction 
and  mode  of  operation  for  each  stroke  is  shown  in  Fig.  1-13.  In 
the  operation  of  this  en- 
gine the  charge  is  drawn 
in  during  the  first  out 
stroke  of  the  piston,  is 
compressed  during  the 
return  stroke,  is  ignited 
with  the  piston  station- 
ary at  the  end  of  the 
stroke  and  with  the  vol- 
ume of  the  charge  con- 
stant. It  expands  during 
the  next  out  stroke  and 
is  exhausted  and  expelled 
-from  the  cylinder  during 
the  next  in  stroke. 

An  engine  of  this 
kind  was  first  described 
by  Beau  de  Rochas  in 
1861,  it  was  first  built 
by  Otto  in  1876.  The 
cycle  on  which  it  oper- 
ates is  for  this  reason 
often  called  the  Beau  de 
Rochas  or  Otto  cycle. 

(b)  Two-stroke  Cycle  Engine.  —  An  internal  combustion  en- 
gine, igniting  as  before,  which  is  used  for  many  purposes,  is  de- 
signed to  perform  the  four  operations  above  referred  to  in  two 
strokes  and  is  known  as  a  two-stroke  cycle  engine  or  a  two-cycle 
engine.  A  common  form  of  such  engine  is  shown  in  Fig.  1-14, 
in  which  form  the  engine  is  in  part  a  double-acting  engine  and 
both  sides  of  the  piston  constitute  closed  chambers.  The  crank 
case  is  made  tight  by  the  use  of  stuffing-boxes  on  the  main  shaft, 
and  the  suction  operation  is  performed  by  the  inward  stroke  of 
the  piston  which  draws  the  charge  into  the  crank  case  through 
the  inlet  /,  where  it  is  partially  compressed  by  the  out  or  return 
stroke  of  the  piston  and  transferred  through  port  a,  which  is  un- 
covered at  the  proper  time  by  the  piston,  to  the  ignition  side  of 


FIG.  1-13.  —  Diagram  of  Four-cycle 
Engine. 


30 


INTERNAL  COMBUSTION  ENGINES 


the  piston.  At  the  same  time  the  charge  of  previously  burned 
gases  is  escaping  through  the  port  E.  The  compression  is 
completed  in  the  working  cylinder  C,  after  the  piston  has 

closed  the  transfer  port  A.  Ignition 
occurs  at  the  beginning  of  the  out 
stroke  and  when  the  piston  and  vol- 
ume in  the  working  cylinder  are  sta- 
tionary as  in  the  preceding  case.  In 
the  action  of  this  engine  suction 
takes  place  below  the  piston  at  the 
same  time  that  compression  takes 
place  above,  and  compression  takes 
place  below  the  piston  at  the  time  of 
expansion  above,  as  shown  by  the 
diagram  of  the  crank  circle  in  the 
figure.  In  certain  large  engines  which 
are  now  made  to  operate  on  the  two- 
stroke  cycle  system  the  suction  and 
preliminary  compression  of  the 
charge,  which  is  performed  in  the 
engine  just  described  by  the  work- 
ing piston,  is  performed  in  a 
separate  cylinder,  the  compression 

being     completed     in     the    working 
FIG.  1-14.— Two-cycle  Engine. 

cylinder. 

The  method  of  igniting  the  charge  in  common  use  will  be 
described  at  length  later  in  the  book.  In  the  class  of  engines  re- 
ferred to  it  consists  of  means  for  firing  the  charge  instantaneously 
when  under  compression,  and  with  its  volume  constant  by  an 
electric  spark,  a  hot  tube,  or  an  open  flame. 

ENGINES  IGNITING  THE  CHARGE  AT  CONSTANT  PRESSURE.  — 
The  only  engine  of  this  class  of  practical  importance  is  the 
Brayton,  although  under  many  conditions  the  Diesel  engine 
ignites  under  constant  pressure.  The  Brayton  engine  was  at 
one  time  used  extensively  in  America  but  is  not  now  manufac- 
tured. In  this  engine  the  combustible  and  air  for  supporting 
combustion  were  supplied  to  the  working  cylinder  under  pressure 
which  remained  constant  until  the  inlet  valve  closed;  the  com- 
bustion taking  place  during  the  admission  of  the  air  and  com- 


INTRODUCTION,  DEFINITIONS,  ETC. 


31 


bustible.  The  work  is  performed  by  pressure  acting  during  in- 
crease of  volume  in  much  the  same  manner  as  in  the  steam  engine. 
In  the  Brayton  engine,  one  form  of  'which  is  shown  in  Fig.  1-15, 
the  compression  is  performed  in  a  compressor  distinct  from  the 
power  end  of  the  working  cylinder,  and  the  heat  is  supplied 
at  constant  pressure.  In  the  figure  B  is  the  working  piston 
arranged  to  move  in  the  cylinder  A.  The  lower  part  of 
the  cylinder  A  is  the  working  cylinder,  the  upper  part  the  air 
compressor  which  is  arranged  to  deliver  air  into  the  reservoir  C. 


FIG.  1-15. — The  Brayton  Engine. 

Oil  is  injected  by  the  pump  G  into  a  vaporizing  device  (shown  on 
a  larger  scale  in  3  of  Fig.  1-15)  when  it  comes  in  contact  with 
compressed  air  from  the  reservoir  C.  The  inlet  valve  b  and  ex- 
haust valve  c  are  operated  by  suitable  cams  on  the  cam  shaft  E. 
ENGINES  IGNITING  THE  CHARGE  AT  CONSTANT  TEMPERA- 
TURE. —  Another  class  of  engine,  patented  by  Diesel,  is  ar- 
ranged to  supply  the  fuel  during  a  portion  of  the  working  stroke 
at  such  a  rate  as  to  maintain  the  temperature  constant,  the 
working  cylinder  having  previously  been  filled  with  air  during 


32 


INTERNAL  COMBUSTION  ENGINES 


a  suction  stroke  and  compressed  during  a  return  stroke.  In  the 
Diesel  engine  the  compression  is  sufficient  to  raise  the  air  to  a 
temperature  high  enough  to  ignite  the  fuel  as  it  enters  the 
working  cylinder. 

The  Brayton  engine  as  above  described  is  a  two-stroke  cycle 
engine  and  the  Diesel  a  four-stroke  cycle  engine,  but  both  engines 
could  be  constructed  to  operate  with  either  cycle. 

17.  The  Engine  Indicator.  —  This  is  an  instrument  de- 
signed to  draw  a  diagram  with  ordinates  proportional  to  the 
pressure  which  acts  inside  the  cylinder  at  each  point  during  the 
working  and  return  stroke  of  the  piston.  It  is  briefly  described 
here  in  order  to  give  the  student  an  idea  of  the  method  of  ob- 
taining the  pressure  volume  diagrams  which  are  frequently  re- 
ferred to  in  the  work. 

It  consists  essentially  of  (1)  a  part  carrying  a  sheet  of  paper 
which  is  moved  by  proper  mechanism  in  corresponding  directions 
and  proportional  to  the  piston  of  the  en- 
gine, and  of  (-2)  a  part  which  carries  a  pen- 
cil which  is  moved  a  distance  proportional 
to  the  pressure  per  square  inch  acting  upon 
the  piston. 

The  engine  -indicator  was  first  designed 
by  James  Watt,  substantially  as  shown  in 
Fig.  1-16.  This  indicator  was  constructed 
with  (1)  a  flat  plate,  D  B,  on  which  paper 
could  be  mounted  which  wras  moved  in 
proportion  to  the  motion  of  the  engine 
piston,  and  (2)  a  cylinder  A  A  which  could 
be  put  in  communication  with  the  working 
cylinder  of  the  engine  by  a  three-way  cock 
H  and  pipe  B.  In  the  cylinder  A  A  was  a 
piston  whose  motion  was  resisted  by  a 
spiral  spring  arranged  to  carry  on  its  piston 
rod  a  pencil  so  constructed  as  to  draw  a 
diagram  on  the  moving  plate  with  ordinates 
proportional  to  the  pressure. 

The  cock  //  can  be  turned  so  as  to  put 
the  cylinder  A  A  in  communication  with  the  air  for  the  purpose 
of  drawing  a  line  showing  the  atmospheric  pressure,  which  is  called 


FIG.  1-16.  —  The  Watt 
Engine  Indicator. 


INTRODUCTION,   DEFINITIONS,  ETC. 


33 


the  "atmospheric  line."  This  simple  form  of  indicator,  although 
containing  the  essential  elements  of  the  modern  indicator,  was  crude 
in  construction  and  gave  results 
which  were  far  from  accurate. 

The  modern  indicator  is  an  in- 
strument of  precision,  and  differs 
principally  from  that  designed  by 
Watt  by  tjie  substitution  (1)  of  an 
oscillating  drum,  called  the  paper 
drum,  for  the  flat  reciprocating 
plate,  for  carrying  the  paper, 
(2)  of  movable  indicator  springs  in 
place  of  a  fixed  one,  making  it 
possible  to  regulate  the  length  of 
the  ordinates,  and  (3)  a  multiply- 
ing pencil  motion  in  place  of  the 
direct  one,  whereby  the  motion  of 
the  pencil  on  the  indicator  drum  is 
made  greater  than  that  of  the  indi- 
cator piston. 


FIG.  1-17.  —  The  Thompson 
Indicator. 


made 


FIG.  1-18.  —  The  Thompson  Indicator. 

A  sectional  and  perspective  view  of  the  Thompson  indicator, 
by   the   American   Steam   Gauge  &  Valve  Company,   is 


34 


INTERNAL  COMBUSTION  ENGINES 


FIG.  1-19.  — The  Crosby 
Indicator. 


shown    in    Figs.    1-17   and   1-18.     A   perspective    view   of    the 
Crosby  indicator,  which  differs  from  the  Thompson   principally 

in  the  construction  of  the  indi- 
cator spring  and  pencil  motion, 
is  shown  in  Fig.  1-19.  For  gas 
engine  work  the  indicator  spring 
is  liable' to  be  injured  by  heat.  To 
lessen  these  difficulties  most  of  the 
makers  supply  indicators  with  ex- 
ternal springs,  as  shown  in  the 
attached  view  of  the  Tabor  indi- 
cator, Fig.  1-20. 

The  authors  have  found  from 
an  extensive  experience  in  indicat- 
ing gas  engines  that  the  indicator 
spring  when  arranged  as  in  Fig. 
1-17  can  be  kept  from  injury  by  surrounding  the  working 
cylinder  with  a  water  jacket  or  cup  filled  with  water. 
The  indicator  cylinder  is  connec- 
ted to  the  working  cylinder  by  a 
pipe  containing  an  indicator  cock, 
which  is  arranged  as  in  the  Watt 
indicator  to  connect  either  with 
the  air  or  the  engine.  The  indi- 
cator drum  is  usually  connected  to 
some  form  of  reducing  motion  by 
the  indicator  cord,  which  will  move 
the  surface  of  the  drum  proportional 
to  the  motion  of  the  piston  and  not 
to  exceed  two  or  three  inches,  re- 
gardless of  the  stroke  of  the  piston. 
Several  forms  of  reducing  motions 
with  schemes  for  connecting  will 
be  shown  in  the  chapter  on  the 
testing  of  gas  engines,  but  will 
not  be  further  referred  to  here. 

The  class  of  engine  indicator  as  described  above  is  not  adapted 
to  take  diagrams  at  extremely  high  speeds  because  of  the  inertia 
of  the  moving  parts  and  because  of  the  error  due  to  stretching 


FIG.    1-20. —The   Tabor    Indi- 
cator with  External  Spring. 


INTRODUCTION,  DEFINITIONS,   ETC. 


35 


of  cords  or  flexible  parts  which  connect  the  paper  drum  to  the 
moving  parts  of  the  engine.  For  high  speeds  the  optical  indica- 
tor is  preferable. 

The  optical  indicator  has  been  designed  so  that  the  only  mov- 
ing part  is  a  small  mirror  which  is  arranged  so  as  to  project  a  ray 
of  light  on  a  ground  glass  screen  or  on  a  photographic  plate. 


FIG.  1-21. — Perspective  View  of  Manograph. 

The  mirror  is  moved  in  one  direction  an  amount  proportional  to 
the  pressure  acting  on  the  piston  of  the  engine,  and  in  a  direction 
at  right  angles  an  amount  in  proportion  to  the  motion  of  the 
piston,  so  that  the  joint  movement  is  proportional  to  the  pressure 
volume  diagram,  the  area  of  which  represents  the  mechanical 


FIG.  1-22. —  Horizontal  Section  of  Manograph. 

work  performed  by  the  working  fluid  in  the  engine  cylinder. 
Such  indicators  are  affected  only  to  a  slight  degree  by  the  rotative 
speed  of  the  engine. 

There  are  two  instruments  of  this  class  on  the  market,  one  the 
Manograph,  manufactured  by  J.  Charpentier,  Rue  de  Lambre, 
20,  Paris,  the  other  the  Optische  Indicator,  constructed  by  the 


36 


INTERNAL  COMBUSTION  ENGINES 


Elsaessische  Electricitaets-Werke,  Strassburg.  A  perspective 
view  of  the  Manograph  mounted  on  a  tripod  is  shown  in  Fig.  1-21, 
a  vertical  section  of  same  in  Fig.  1-22;  a  detailed  view  of  the  mirror 
and  engine  connections  are  shown  in  Figs.  1-23  and  1-24. 


FIG.  1-23.  —  Section  of  Manograph 
Mirror. 

The  general  construction  is  that  of  a  photographic  camera 
connected  to  the  engine  by  tube  T,  and  by  flexible  shaft  R  con- 


FIG.  1-24.  —  Manograph  Engine 
Connection. 

nected  to  the  main  shaft  of  the  engine.  An  acetylene  or  electric 
lamp  is  located  at  G  and  its  ray  of  light  is  projected  through  a 
perforated  diaphragm  to  a  prism,  H,  and  thence  to  mirror  N, 
at  the  back  of  the  camera.  The  mirror  N,  supported  on  springs, 


INTRODUCTION,   DEFINITIONS,  ETC. 


37 


Fig.  1-23,  is  connected  by  a  pin  with  the  diaphragm  M,  which  is 
in  communication  with  the  engine  cylinder,  so  as  to  be  tilted  in 
one  direction  an  amount  proportional  to  the  change  of  pressure 
in  the  engine  cylinder.  The  mirror  N  is  also  tilted  in  a  direction 
at  right  angles  to  the  first  motion  by  means  of  a  crank  with  lever 
connection  which  is  rotated  from  the  shaft  in  proportion  to  the 
motion  of  the  engine.  The  motion  of  the  small  crank  can  be  set 


FIG.  1-25  —  Diagram  with  Manograph. 

in  phase  with  that  of  the  engine  crank  by  the  thumb  screw  F  so 
that  it  will  give  a  motion  directly  proportional  to  the  piston  of 
the  engine.  To  make  the  errors  as  small  as  possible  the  angular 
motion  of  the  mirror  is  made  very  small.  The  pressure  scale  of 
the  manograph  should  be  determined  by  carefully  comparing  the 
photographic  diagram  with  a  known  pressure.  The  instrument 


FIG.  1-26.  —  Optical  Indicator. 

is  arranged  to  give  a  diagram  which  would  have  exactly  correct 
proportions  when  the  connecting  rod  has  a  length  4.5  times  that 
of  the  crank,  which  is  nearly  the  average  proportions  in  actual 
practice  and  would  make  the  resulting  error  small  for  other 
conditions. 

Figure  1-25  represents  a  diagram  taken  with  the  Manograph 
from  an  engine  making  1500"  turns  per  minute  and  giving  a  maxi- 
mum pressure  corresponding  to  158  pounds  per  square  inch. 


38  INTERNAL  COMBUSTION  ENGINES 

The  Optische  Indicator  differs  from  the  Manograph  princi- 
pally in  details  of  construction.  Its  general  appearance  is  shown 
in  Fig.  1-26.  A  diagram  taken  from  a  motor  operated  with 
gasoline  making  1000  turns  per  minute  is  shown  in  Fig.  1-27, 
the  pressure  scale  of  which  is  about  120  pounds  per  square 
inch. 


FIG.  1-27.  —  Diagram   with 
Optical  Indicator. 

18.  Indicated    and    Brake    or    Delivered    Horse-Power.  — 

The  indicated  horse-power  which  is  generally  denoted  by  the 
symbol  I.  H.P.  is  proportional  to  the  area  of  the  diagram  obtained 
by  use  of  the  engine  indicator,  since  this  diagram  has  ordi- 
nates  which  are  proportional  to  the  pressures  acting  upon 
the  engine  piston  at  each  point  during  the  working  and  return 
strokes,  and  abscissa  proportional  to  the  corresponding  space 
moved  through  by  the  engine  piston. 

The  indicated  horse-power   (I.  H.  P.)  is  computed  by  use  of 
the  formula 

plan 


I.  H.  P.  = 


33000 


in  which  p  =  the  mean  effective  pressure  (m.  e.  p.)  for  the 

cycle   of   operation,  acting  on   each   square 
inch  of  the  piston. 
I  =  length  of  stroke  in  feet. 
a  =  net  area  of  piston  in  square  inches. 
n  =  number  of  cycles  per  minute. 
33,000  =  number   of   foot-pounds    per    minute   in   one 

horse-power. 
The  mean  effective  pressure  (m.  e.  p.)  is  the  mean  ordinate 


INTRODUCTION,   DEFINITIONS,  ETC.  39 

for  all  the  strokes  constituting  the  cycle  multiplied  by  the 
proper  pressure  scale;  it  is  best  obtained  by  finding  the  net  area 
by  use  of  a  planimeter  (an  instrument  which  will  be  described 
later),  which  is  to  be  divided  by  the  length  of  the  diagram  and 
multiplied  by  the  scale  of  the  indicator  spring.  The  other 
quantities  in  the  formulae  depend  upon  the  dimensions  and  speed 
of  the  engine. 

The  brake  or  dynametric  horse-power,  for  which  the  symbol 
in  this  work  will  be  D.  H.  P.,  is  that  delivered   from  the  main 
shaft  of  the  engine  and  is  consequently  less  than  the  indicated    V 
horse-power   by  an   amount  equal    to    the   engine   friction   and 
internal  losses. 

The  brake  horse-power  is  usually  measured  by  use  of  a  spe- 
cial form  of  absorption  dynamometer  known  as  the  Prony  brake. 
Various  forms  of  this  brake  have  been  employed,  of  which 


FIG.  1-28.  —  A  Prony  Brake. 

two  only  are  considered  in  this  place.  One  form  is  shown  in  the 
diagram  Fig.  1-28,  which  consists  of  a  series  of  blocks  connected 
by  a  leather  strap  or  strip  of  iron  and  arranged  so  as  to  rub  on 
the  surface  of  a  wheel  attached  to  the  main  shaft.  The  brake  is 
provided  with  two  arms,  the  free  end  of  which  rests  on  a  pair  of 
scales.  The  amount  of  friction  may  be  varied  by  use  of  a  hand 
wheel  or  similar  device  as  shown  at  S.  The  horizontal  distance 
from  the  center  of  the  wheel  to  the  end  of  the  arms  is  known  as 
the  arm  of  the  brake  and  is  denoted  in  the  formulae  which  fol- 
low by  a.  In  the  use  of  the  brake  the  load  is  applied  by  turning 
the  screw  and  is  measured  by  the  reading  on  the  weighing  scale. 
In  a  brake  with  the  arm  on  one  side  only,  as  shown  in  the  figure, 
the  amount  required  to  balance  the  overhanging  brake  arm 
must  be  deducted  from  the  reading  of  the  scales  to  give  the  net 
load. 


40  INTERNAL  COMBUSTION   ENGINES 

The  horse-power  is  calculated  from  the  formula 
D   TT   p       2  TT  a  n  W 

33000 

in  which  n    =  number  of  revolutions  per  minute. 
a    =  the  brake  arm  in  feet. 

W  =  the  net  load  on  scales  corrected  for  unbalanced 
effect  of  brake. 

Another  form  of  brake  is  shown  in  diagram,  Fig.  1-29,  which 
is  convenient  for  testing  small  engines.  It 
consists  of  a  rope  or  strap  which  makes 
one  or  more  turns  around  the  wheel,  the 
tension  or  pull  on  both  ends  of  which  must 
be  known  or  measured.  In  the  form  shown 
a  weight  of  known  amount,  w,  is  applied 
at  one  end,  and  a  spring  balance  is  em- 
ployed to  measure  the  resistance  at  the 
other  end. 

The  formula  for  this  brake  is  as  fol- 

lows: 
FIG.    1-29.  —The  Rope  0  /TJ7        x 

D-H-^2" 


in  which  r     =  radius  of  the  wheel  in  feet  to  center  of  strap. 
W  =  the  principal  scale  reading. 
w    =  the  lesser  scale  reading  or  weight  carried. 

In  a  modification  of  this  brake  the  principal  tension  is  received 
by  a  framework  resting  on  a  pair  of  scales,  and  the  smaller  resist- 
ance is  absorbed  by  an  upward  pull  on  the  platform  of  the  same 
scales.  With  this  arrangement  the  scale  reading  gives  directly 
the  difference  of  weights  W  —  w. 

In  the  use  of  the  Prony  brake  heat  is  generated  equivalent  to 
the  mechanical  work  absorbed.  If  the  load  is  heavy  it  will  be 
necessary  to  circulate  water  or  some  other  heat-removing  fluid 
inside  of  the  rim  of  the  revolving  wheel  or  in  some  equivalent 
place. 

19.  Forms  of  Indicator  Diagrams.  —  A  few  of  the  typical 
forms  of  indicator  diagrams  are  considered  in  this  place  for  the 
purpose  of  making  the  student  familiar  with  the  subject.  They 
will  be  discussed  at  length  later  in  the  work. 


INTRODUCTION,   DEFINITIONS,  ETC. 


41 


Figure  1-30  is  a  hypothetical  diagram  of  a  four-cycle  explosion 
engine  with  the  events  which  take  place  on  the  various  strokes 
marked.  Thus  the  suction  stroke  is  represented  by  d  e,  the  com- 
pression by  e  /,  the  explosion  by  /  a,  the  expansion  by  a  b, 
the  exhaust  by  6  c  d.  The  atmospheric  line  not  clearly  shown  in 
the  diagram  would  occupy  a  position  intermediate  between  c  d 


HYPOTHETICAL   DIAGRAM, 
showing  Cycle. 


FIG.   1-30.  —  Four-cycle  Engine. 

and  e  d.  The  lines  c  d  and  e  d  on  the  indicator  usually  coincide 
with  the  atmospheric  line  for  the  reason  that  the  spring  used  is 
too  stiff  to  show  such  small  variations  in  pressure  as  exist  between 
the  atmospheric  line  and  the  exhaust  and  suction  lines. 

Figure  1-31  shows  diagrams  of  a  two-cycle  explosion  engine 
in  which  the  upper  diagram,  abcf,  is  taken  in  the  working  cyl- 


FIG.  1-31.  —  Two-cycle  Engine  Diagram. 

inder,  and  the  lower  diagram,  e'  /',  in  the  compressor.  In  this 
diagram  the  net  work  is  the  difference  between  that  shown  on 
the  first  diagram  and  that  on  the  second. 

Figures  1-32  and  1-33  are  diagrams  from  a  Brayton  or  constant 
pressure  engine,  Fig.  1-32  being  taken  from  the  working  cylinder 
and  Fig.  1-33  from  the  compression  cylinder.  It  will  be  noted 


42 


INTERNAL  COMBUSTION  ENGINES 


from  Fig.  1-32  that  the  pressure  remains  constant  from  a  to  a', 
at  which  time  communication  is  cut  off  from  the  compressor, 
after  which  the  fluid  expands  from  a'  to  c  in  much  the  same 


FIG.  1-32.  —  Diagram  from  Brayton  Working  Cylinder. 

manner  as  in  the  steam  engine.     The  net  work  is  proportional 
to  the  difference  of  the  areas  of  the  two  diagrams. 


FIG.  1-33.  —  Diagram  from  Brayton  Compressor. 

Figure  1-34  is  a  diagram  from  a  Diesel  engine  in  which  the 
temperature  is  supposed  to  be  constant  during  that  portion  of 
the  stroke  represented  by  a  b,  during  which  time  fuel  is  being  sup- 
plied to  the  working  cylinder. 


FIG.  1-34.  —  Diesel  Engine  Diagram. 

Figure  1-35  is  a  diagram  from  a  steam  engine,  the  expansion 
line  of  which  as  referred  to  an  hyperbola,  c  e  f  g  h,  which  is  asymp- 
totic to  the  line  of  no  pressure,  C  D,  and  of  no  volume,  C  B. 
Points  in  the  hyperbola  are  obtained  if  the  initial  point,  c,  is 


INTRODUCTION,  DEFINITIONS,  ETC. 


43 


known,  by  drawing  a  vertical  from  c;  then  from  C  draw  diagonals 
crossing  c  b  and  A  B.  The  intersection  of  a  horizontal  line  from 
the  intersection  of  the  diagonal  and  c  b,  with  a  vertical  line  from 


B  rr 


FIG.  1-35.  —  Method  of  Drawing  Hyperbola. 

the  intersection  of  the  same  diagonal  and  the  line  A  B,  give  points 
in  the  hyperbola. 

Another  method  of  drawing  an  hyperbola  is  shown  in  Fig.  1-36, 


d' 


FIG.  1-36.  —  Method  of  Drawing  an  Hyperbola. 

which  represents  an  indicator  diagram  referred  to  lines  of  no 
volume  and  no  pressure.  This  method  is  founded  on  the  prin- 
ciple that  the  intercepts  made  by  a  straight  line  intersecting  an 


44  INTERNAL   COMBUSTION  ENGINES 

hyperbola  and  its  asymptotes  are  equal.  Beginning  at  any 
point  as  a,  draw  the  straight  line,  a'  bf,  and  lay  off  from  the  line 
CD,  b'  b  equal  to  a'  a,  then  will  b  be  a  point  in  the  hyper- 
bola. Draw  a  similar  line  through  b  as  c'  d'  and  find  another 
point  as  c.  Repeat  the  method  until  all  the  points  required  for 
drawing  the  curve  are  found. 

The  hyperbola  is  a  useful  line  of  reference  in  connection  with 
indicator  diagrams.  As  will  be  shown  later,  it  represents  the 
condition  of  isothermal  expansion  in  the  gas  engine. 


CHAPTER  II 

THERMODYNAMICS    OF    THE    GAS    ENGINE 

i.  Notation.  —  In  order  to  comprehend  the  limitations  of 
the  actual  engine  it  is  necessary  to  understand  how  the  working 
fluid  behaves  when  subject  to  definite  changes  in  an  engine  un- 
affected by  friction  or  mechanical  limitations,  and  we  will  for 
that  reason  give  attention  to  the  theoretical  considerations  relat- 
ting  to  the  " internal  combustion  engine"  which  forms  part  of 
the  science  of  Thermodynamics. 

In  the  consideration  of  the  theoretical  action  of  a  perfect 
engine  the  following  symbols  will  be  used: 

A    =  the  reciprocal  of  the  mechanical  equivalent  of  heat. 
a     =  the  absolute  temperature  of  the  freezing-point  =  273  C.  or  492  F. 
Cp   =  the  specific  heat  of  constant  pressure  in  heat  units. 
Cv    =  the  specific  heat  of  constant  volume  in  heat  units. 

J     =  mechanical  equivalent  of  heat  =  778  in  foot-pounds  =  426  K.  G.  M. 
Kp  =  specific  heat  of  constant  pressure  in  mechanical  units. 
Kv  =  the  mechanical  heat  at  constant  volume  in  mechanical  units. 
p     =  absolute  pressure  for  condition  denoted  by  postscript. 
Po   =  absolute  pressure  at  freezing-point. 
Q     =  the  total  heat  of  a  given  mass. 
R    =  a  constant  for  a  given  gas. 
T    =  absolute  temperature. 

t      =  temperature  Fahrenheit  or  Centigrade  as  marked. 
•o     =  volume  of  a  given  mass  of  gas,  its  condition  being  denoted  by  postscipt. 
VQ    =  the  volume  of  a  given  mass  of  gas  at  freezing-point. 
W   =  the  mechanical  work  performed  in  mechanical  units. 
W  =  the  mechanical  work  in  heat  units. 

a     =  the  coefficient  of  expansion  of  a  perfect  gas  =  the  reciprocal  of  a. 
7     =  specific  heat  of  constant  pressure  divided  by  the  specific  heat  of  constant 
volume. 

2.  Characteristics  of  Perfect  Gases.  —  In  an  internal 
combustion  engine  the  work  is  produced  by  the  change  of  volume 
and  pressure  of  a  gaseous  mixture  composed  of  atmospheric  air 

45 


46  INTERNAL  COMBUSTION   ENGINES 

and  the  various  products  of  combustion.  This  gas  mixture, 
within  the  working  limits  of  temperature,  is  obedient  to  the 
laws  of  the  perfect  gases,  and  for  that  reason  in  any  theory  of  the 
internal  combustion  engine  we  are  principally  concerned  with 
such  laws  and  with  the  changes  of  volume  and  pressure  in  a  per- 
fect gas,  in  relation  to  its  change  of  temperature. 

By  combining  Boyle's  law  with  Gay-Lussac's  law  it  is  learned 
that  the  product  of  pressure  and  volume  of  a  given  mass  of  a 
perfect  gas  varies  directly  as  its  absolute  temperature,  that  is: 

pv  =  pQvQ   (1  +  a  t)  (1) 

in  which  p  equals  the  absolute  pressure  and  v  the  volume  of  a 
given  mass  of  gas  at  a  temperature,  t,  above  the  freezing-point, 
p0  and  v0  represent  the  pressure  and  volume  of  the  same  mass 
at  the  freezing-point,  and  a  represents  the  coefficient  of  expan- 
sion of  the  gas  per  degree  of  absolute  temperature.  As  has 
already  been  shown  a  will  equal  when  expressed  in  the  Centi- 
grade system  the  reciprocal  of  273  and  when  expressed  in  the 
Fahrenheit  system  the  reciprocal  of  492.  If  we  denote  the 
number  of  degrees  between  the  freezing-point  and  absolute  zero 
by  a,  then  from  the  preceding  explanation  a  will  equal  the  re- 
ciprocal of  a.  If  we  denote  the  absolute  temperature  by  T  we 

shall  have 

T  =  a  +  t.  (2) 

substituting  —  for  a  in  equation  (1)  we  have 


13  V 

in  the  above  equation  -  —  is  a  constant  for  each  gas. 


a 
then  we  have 


Let  R  =  (4) 

a 

p,  =  RT.  (5) 


The  above  equation  may  be  considered  the  characteristic 
equation  of  a  perfect  gas,  since  it  shows  the  relations  between  the 
pressure,  volume  and  absolute  temperature. 

R  is  a  constant  which  depends  on  the  nature  of  the  gas  and 


THERMODYNAMICS  OF  THE  GAS  ENGINE 


47 


can  be  computed  if  the  specific  pressure,  p0,  and  specific  volume, 
v0  at  standard  pressures  and  temperatures  are  known. 

It  follows  from  the  above  that,  p^  =  RT1}  from  which  by 
comparing  with  (5) 

po'.p&t  ::7\  :T  (5a) 

The  specific  pressure  p0  is  the  weight  of  the  atmosphere  at  the 
freezing-point  under  normal  conditions;  it  is  equivalent  to  that  of 
a  column  of  mercury  760  mm.  high  (29.921  inches).  This  re- 
duced to  pressure  per  unit  of  area  is 

p0  =  10333  kilograms  per  square  meter; 
or  in  English  units, 


p0  =  31  fr6.83     pounds  per  square  foot. 
,  =      14.696    pounds  per  square  inch. 

=     29.921    inches  of  mercury. 

The  specific  volume  is  determined  from  the  density  of  the 
gas.  The  following  table  gives  the  specific  volume  in  Metric  and 
English  measures  for  some  of  the  more  common  gases: 


VALUE  OF  v0  AT  LAT.  45° 


Cubic  meters  per 
Kilogram 

Cubic  feet 
per  Pound 

Air 

0  7735327 

12  3909 

Nitrogen  (N)  

0.7963291 

12.7561 

Oxygen  (O)             

0.6996231 

11  2070 

Hydrogen  (H) 

1  116705 

178  881 

Carbonic  Acid  (CO?) 

0  5058741 

8  10324 

By  substituting  the  values  of  p0v0,  and  a  in  the  equation  R  = 
—  the  value  of  R  can  be  found. 


Thus  for  air,  in  French  units 

R  =  10333    X  0.77353  -  273  =  29.20  ; 
in  English  units 

R  =  2116.3  X     12.391  -  492  =  53.22. 


48  INTERNAL  COMBUSTION   ENGINES 

The  following  table  gives  values  of  R  for  a  few  gases : 


VALUES  OF  R 

v    English            |              Metric 

Hydrogen  (H)                             

770.3 

48.74 
35.41 
53.22 

422.68 
26.475 
19.43 
29.20 

Oxvffen  fO^ 

Carbon-dioxide  (CO2)    

Air                                    

The  following  table  showing  the  specific  heat  of  the  ordinary 
gases  is  inserted  here  for  convenience. 


TABLE  OF  SPECIFIC  HEATS 


SPECIFK 

:  HEAT 

£* 

NAME  OF  GAS 

SYMBOL 

Constant 
Pressure 

CP 

Constant 
Volume 

cv 

CV 

y 

Air 

0  2375 

0  1684 

1  406 

Oxvffcn 

o 

0  2175 

0  1552 

1  403 

Nitrogen  
Hydrogen 

N 
H 

0.2438 
3  4090 

0.1727 
2  4110 

1.416 
1  414 

Nitric  oxide  

NO 

0.2317 

0.1652 

1  402 

Carbonic  oxide  
Carbon  dioxide 

CO 
CO2 

0.2450 
0  2000 

0.1736 
0  1550 

1.413 
1  261 

Steam    

H2O  (saturated) 

0  4805 

0  3700 

1  298 

Methane  
Acetylene  
Disulphide  carbon  
Olefiant  gas 

CH4 
C2H2 
CS2 
C  H 

0.5930 
0.3460 
0.1569 
0  4040 

0.4680 
0.2700 
0.1310 
0  3330 

1.198 
1  125 

Ammonia.  .  .-.  . 

24 

NHj 

05084 

0  3910 

1  300 

Alcohol 

CH0Ofl 

04534 

0  4100 

1  150 

A   2     6 

As  before  noted,  the  specific  heat  of  gases  increases  with  the 
temperature  and  possibly  also  with  the  pressure,  which  law  will 
be  referred  to  in  discussing  the  application  to  special  cases.  The 
expanding  products  of  combustion  are  composed  of  N,  CO2  H2O, 
O,  and  possibly  a  trace  of  NO.  For  approximate  computations 
the  value  of  Cp/Cv  for  the  burned  gases  may  be  taken  at  1.37. 

3.  General  Relations  of  Heat  Transmission  to  Changes  of 
Volume  and  Pressure.  —  When  a  quantity  of  heat  dQ  is  sup- 
plied to  a  mass  of  gas  it  produces  a  complex  result;  the  heat 


THERMODYNAMICS  OF  THE  GAS  ENGINE  49 

warms  the  gas  and  raises  its  temperature,  at  the  same  time  per- 
forming internal  work  by  overcoming  the  molecular  forces;  it 
then  develops  external  work,  which  is  made  apparent  by  the 
expansion  of  the  gas  against  an  external  resistance.  Denoting 
by  dU  the  quantity  of  heat  employed  in  warming  the  gas  and  in 
molecular  work  we  will  have 

dQ  =  dU  +  Apdv, 

in  which  pdv  is  the  external  work  expressed  in  mechanical  units 
and  A  pdv  its  equivalent  in  heat  units. 

In  the  operation  of  a  gas  engine  the  mass  of  gas  constituting 
the  working  substance  expands  during  each  cycle  from  one 
volume  to  another,  passing  through  a  series  of  successive  changes 
of  volume  and  pressure,  and  finally  returns  to  its  initial  state. 
It  is  evident  that  when  the-mass  returns  to  its  initial  state  that 

the  quantity  represented  byfdU  is  equal  to  zero.  For  this  condi- 

tion we  shall  have 

dQ  =  A  pdv. 

Calling  U  the  internal  heat  of  the  gas,  which  has  already  been 
shown  to  be  a  function  of  the  volume  pressure  and  temperature, 

we  have  TT       ,  . 

U  =  f(v.  p.  t.). 

Since  t  can  be  determined  from  the  values  of  p  and  v  as  indicated 
in  equation  5,  we  can  consider  that  in  practice  U  is  a  function 
only  of  v  and  p  and  may  write 

U  =  }  (v.  p.). 

The  increase  of  internal  heat  for  a  variation  of  volume  dv 
and  of  pressure  d  p  may  be  expressed  as  a  total  differential  of  the 
function,  /,  and  we  have 


By  substituting  the  above  value  in  the  expression  d  Q  the  thermal 
state  of  the  gas  may  be  represented  as  follows: 


or 


50  INTERNAL  COMBUSTION  ENGINES 

It  may  be  noted  that  the  above  equation  cannot  be  integrated 
in  its  present  form  unless  Q  can  be  expressed  as  a  function  of  the 
initial  and  final  volumes  and  pressures  of  the  gas.  This  demon- 
strates that  the  expenditure  of  heat  required  to  make  a  gas  pass 
from  one  state  to  another  cannot  be  deduced  from  a  knowledge 
of  the  extreme  states,  if  one  does  not  know  the  order  and  relation 
of  the  intermediate  states. 

The  heat  transferred  at  constant  volume  is  equal  to  the  specific 
heat  Cv  multiplied  by  the  change  of  temperature.  That  is,  Q  = 
Cv  (Tl  —  T),  from  which  dQ  =  Cvdt.  For  a  similar  reason  that 
transferred  at  constant  pressure 

'Q    =  Cp(T,-T} 
dQ  =  Cpdt. 

For  the  condition  of  transfer  of  heat  at  constant  volume,  dv  of 
equation  (7)  will  equal  0,  and  equation  (7)  will  become 


Since  the  heat  interchange  for  this  case  takes  place  at  constant 
volume,  it  has  been  shown  that 

dQ  =  C^dt. 
By  placing  these  two  values  of  dQ  equal  we  have 

c  -  -  -  (m 

C>      Sp 

*TT 

from  which  the  value  of  g—  for  heat  interchanges  at  constant 

volume  can  be  found. 

For  the  transfer  of  heat  at  constant  pressure  the  temperature 
changes  take  place  without  change  of  pressure,  in  which  case 
d  p  of  equation  (7)  =  0,  and  we  have  by  substitution 


Since  the  heat  interchange  for  this  case  takes  place  at  constant 
pressure,  dQ  =  Cpdt,  and  by  substitution 

dt       SU 


THERMODYNAMICS  OF  THE  GAS  ENGINE  51 

&TT 
from  which  the  value  of  y-  for  heat  transformation  at  constant 

pressure  can  be  obtained.     Substituting  the  values  of  eq.  (8)  and 
(9)  in  eq.  (7)  we  have 

dQ  =  C^dp  +  Cpfvdv  (10) 

which   gives  the  value  of  the  heat  interchange  for  successive 
change  of  pressure  and  volume.     This  can  be  reduced  as  follows: 
From  eq.  (5),  pv  =  RT,  hence  vdp  =  Rdt  when  v  is  constant, 
and  pdv  =  Rdt  when  p  is  constant.     From  this  it  follows  that 

Bt       v         ,  Bt       p 

•£-  =  D»  and  T  =  D 
Bp      R  W      R 

Substituting  the  above  values  in  eq.  (10)  we  have 

dQ  =  |  (Cvvdp  +  Cppdv)  (11) 

Now,  from  eq.  (5)  ,  we  obtain  by  complete  differentiation 

pdv  +  vdp  =  Rdt,  from  which  vdp  —  Rdt  —  pdv 
Substituting  this  in  eq.  (1  1)  we  may  write 

dQ  =  jJCv(Rdt  -  pdv)  +  Cppdv] 


But  from  eq.  (5)  p  _  T 

R~  v 

hence  finally  ~  x  T  , 

dQ  =  C^dt  +  (Cp  -  Cv)  -  dv  (lla) 

4.  Transformation  to  Different  States.  —  The  modes  of  trans- 
formation from  one  state  to  another  depend  upon  the  relation  of 
p  and  v  at  different  points,  T  being  always  determined,  by  the 
relation  of  p  to  v,  from  eq.  (5). 

For  simplicity  of  treatment  and  for  producing  a  standard  for 
comparison  it  is  assumed  that  the  changes  in  the  relations  of 
volume,  pressure,  and  temperature  take  place  with  one  of  the 
variables  constant  in  the  general  equation  (5a)  ,  p.  47. 

Thus,  if  the  volume  remains  constant  during  the  change,  we 
have  v  =  vlf  and 

-  (12) 


52  INTERNAL  COMBUSTION   ENGINES 

which  is  the  equation  for  constant-  volume  conditions.     If  the 
pressure  remain  constant,  p  =  pl  and 

V  -2-  (13) 


which  is  the  equation  for  constant-pressure  conditions.  If  the 
temperature  remain  constant,  which  latter  is  termed  an  isothermal 
condition,  T  =  7\. 

i-LJt  (14) 

Pi      v 

which  is  the  equation  of  an  isothermal  line  for  a  perfect  gas  in  a 
pressure-  volume  diagram. 

Another  standard  of  comparison  is  the  transformation  in 
pressure,  volume  or  temperature  which  takes  place  without  gain 
or  loss  of  heat.  This  latter  condition  is  called  adiabatic  and  cor- 
responds to  that  of  constant  entropy.  It  represents  the  conditions 
of  the  equation  (11)  when  dQ  =  0,  in  which  case 

Cvvdp  +  Cppdv  =  0 

C1 

vdp  +  -~rpdv  =  0 

Cy 

C1 

Substitute  y  for  -^,  then 

CT, 

vdp  -f-  ypdv  =  0. 
which  integrated  between  the  limits  plvl  and  pv  gives 

-7  log.  •) 


from  which  p^  —  pvy  =  constant  (15) 

which  is  the  equation  of  an  adiabatic  line  for  a  perfect  gas  in  a 
pressure-  volume  diagram. 

The  equation  for  adiabatic  transformation  in  terms  of  v  and  T 
can  be  obtained  by  substituting  for  p  and  p^  the  values  as  given 
in  (5a)  and  reducing,  which  will  give 

TV-'  -  T>  -'  ^ 

In  a  similar  manner  the  adiabatic  equation  in  terms  of  p  and  T 
can  be  obtained,  which  is  as  follows: 


THERMODYNAMICS  OF  THE  GAS  ENGINE  53 

5.  Work  Performed  in  Isothermal  Expansion.  —  The  work, 
W,  performed  when  the  gas  expands  isothermally  from  an 
initial  volume,  v  to  a  volume  vl  can  be  calculated  as  follows  : 

The  general  formula  for  mechanical  work  is 

W  -i  fpdv 
but  as  pv  =  p^  for  isothermal  expansion 


/Virlii  -ji 

-p,»,iog.  (is) 


Since  pv  =  plvl  =  RT  this  may  be  written 


The  heat  applied  during  isothermal  expansion  can  be  obtained  by 
making  dt  =  0  and  T  a  constant  in  (11  a)  and  integrating.  We 
will  have 

Q=(CP-  C\)T  P  d    =  (CP-CV)T  \oge^  =  ARTloge  -'       (19) 


This  value  being  the  same  as  that  of  the  external  work  indicates 
that  the  heat  applied  during  isothermal  expansion  is  equivalent  to 
the  external  work  performed. 

It  will  be  noted  from  (18)  that  an  infinite  increase  in  isother- 
mal expansion  will  lead  to  an  infinite  amount  of  work.  Thus 
in  the  equation 

W  =  pv  loge  — 

if  v1  be  made  equal  to  infinity  the  value  of  W  also  becomes  infinite. 

6.   Work   Performed   in   Adiabatic    Expansion.  —  The   work 

performed  when  the  gas  expands  adiabatically  from   an  initial 

volume,  vl  to  a  volume,  v2,  can  be  found  by  substituting  the  value 

°f  P  =  —^  from  formula  (15)  as  follows: 

dv 
W 


pi  F-'i 

=    I     pdv  =  p.v  I 
Jv     l  ^  l  Jv 


54  INTERNAL  COMBUSTION    ENGINES 


1  -  ~  '* 


Therefore  W  =  ^  J  1  -  (£)        ^  (20) 

For  infinite  adiabatic.  expansion  the  work,  W,  does  not  become 
infinite  as  in  isothermal  expansion,  since  for  this  case  —  =  0,  and 

W 


7-1 

7.  Relations  of  Heat  to  Entropy.  —  The  heat  transfor- 
mations can  be  expressed  as  a  function  of  the  absolute  tempera- 
ture and  entropy,  which  expression  possesses  some  advantages 
for  tracing  heat  interchanges  over  the  pressure- volume  equations. 

For  this  case  the  variables  in  the  equation  become  tempera- 
ture, T,  and  entropy,  <£,  instead  of  v  and  p  as  in  the  preceding 
cases;  in  the  diagram  representing  such  conditions,  horizontal 
lines  would  represent  equal  temperatures  or  isothermal  conditions, 
while  vertical  lines  would  represent  equal  entropy  or  adiabatic 
conditions.  The  ordinates  in  such  a  diagram  would  then  repre- 
sent temperature,  T,  and  the  abscissa  entropy,  <f>. 

Since  the  heat  interchange  d  Q  is  equal  to  the  product  of  the 
absolute  temperature  into  the  corresponding  change  of  entropy, 

we  have 

dQ  = 


•*-¥ 


For  gases,  if  heat  is  supplied  at  constant  pressure  dQ  =  Cpdt 

r  (21) 


8.  Carnot  or  Reversible  Engine,  Second  Law  of  Ther- 
modynamics. —  A  reversible  engine  is  one  that  may  be  run  in 
one  direction  so  as  to  transform  heat  into  work,  or  in  the  opposite 
direction  so  as  to  transform  work  into  heat. 

No  actual  heat  engine  is  built  in  this  manner,  since  such  an 
hypothesis  requires  that  all  the  gases  exhausted  shall  pass 
through  all  the  states  in  a  reversed  direction  during  compression 
and  return  to  the  initial  state,  which,  because  of  the  chemical 


THERMODYNAMICS  OF  THE  GAS  ENGINE  55 

changes  during  combustion,  is  impossible  in  the  internal  combus- 
tion engine.     The  internal  combustion  engine  can  be  considered 
as  approximating   the   theoretical   reversible  engine,  which  thus 
becomes  useful  as  a  standard  of  comparison. 
For  the  cycle  of  a  reversible  engine 


This  is  the  highest  attainable  result  with  any  heat  engine,  since  it 
indicates  that  the  heat  transferred  into  work  from  motion  in 
one  direction  would  be  returned  to  its  source  by  an  equal  amount 
of  work  applied  to  drive  the  engine  in  an  opposite  direction. 
The  above  statement  is  Carnot's  principle,  which  is  often  called 
the  Second  Law  of  Thermodynamics.  It  follows  from  this:* 

(1)  All  reversible  engines  working  between  the  same  source 
of  heat  and  refrigerator  have  equal  efficiencies. 

(2)  The  efficiency  of  a  reversible  engine  is  independent  of 
the  working  substance. 

(3)  A  self-acting  machine  cannot  transfer  heat  from  one  body 
to  another  at  a  higher  temperature. 

It  further  follows  from  this  that  for  any  irreversible  engine 
cycle  the  work  for  a  given  expenditure  of  heat  is  less  than  for  a 
reversible  engine;  that  is, 


in   which   N   represents   the   mechanical    results    of  the    work 
performed. 

9.  Graphical  Relations.  —  The  relations  of  the  heat  inter- 
changes to  the  transformations  of  pressure,  volume,  and  tempera- 
ture will  be  more  clearly  understood  by  reference  to  a  diagram. 
The  pressure- volume  diagram,  which  has  for  its  ordinates  lines 
corresponding  to  pressure  and  for  its  abscissae  distance  corre- 
sponding to  volumes,  shows  the  conditions  of  uniform  pressure 
by  a  horizontal  line  and  of  constant  volume  by  a  vertical  line. 
On  this  diagram  an  isothermal  line  is  represented  by  equation 
(14),  pv  =  p^v^  which  is  the  equation  of  an  equilateral  hyperbola 
of  which  the  axes  are  the  lines  of  zero  volume  and  the  line  of  zero 
pressure.  Two  methods  of  drawing  the  hyperbola  have  been 
*Peabody's  Thermodynamics,  page  30 


56 


INTERNAL  COMBUSTION  ENGINES 


given  in  Art.  19,  Chapter  I.  In  the  case  of  a  steam  engine  it  will 
be  remembered  that  an  isothermal  condition  is  represented  by  an 
equal  pressure  line. 

The  equation  of  an  adiabatic  line  on  a  pressure-volume  dia- 
gram, as  given  in  (15)  is  log  —  =  y  log  -.    The  values  of  the  coor- 

Pi  v 

dinates  for  drawing  this  curve  can  be  found  by  assuming  values 

11 

of — -and  finding  the  corresponding  values,  by  use  of  a  table  of 

T) 

Naperian  logarithms,  of  — .     A  table  giving  the  values  of  y  for 

Pi 
different  gases  has  been  given.     It   is  usually  assumed   as   1.37 

for  gas  engines  and  is  subject  to  some  correction  for  changes  due 
to  rise  of  temperature.  The  general  relations  of  isothermal  and 
adiabatic  lines  to  pressure,  volume  and  temperature  is  shown  on 
the  diagram  Fig.  2-1. 


10   20  30   40   50  60   70  80   90  100  10 


30   40   50  60  70  80.  90  200% 


1  CU.D'IC  foot.  2  cubic  feet. 

FIG.  2-1. — Relations  of  Isothermal  and  Adiabatic  Curves. 


Figure  2-1  shows  isothermal  and  adiabatic  expansion  and  com- 
pression lines  drawn  from  the  same  points.  This  diagram  shows 
that  for  a  given  number  of  expansions  the  adiabatic  line  falls 


THERMODYNAMICS  OF  THE  GAS  ENGINE 


57 


below  the  isothermal  line,  and  also  that  the  area  between  the 
adiabatic  line  and  the  base  line  is  less  than  that  between  the 
isothermal  and  the  base  line.  As  this  area  represents  the  exter- 
nal work  performed,  it  indicates  that  for  a  given  number  of  ex- 
pansions the  work  is  greater  in  isothermal  than  in  adiabatic 
expansion,  which  also  follows  from  the  demonstrations  which 
have  been  given. 


150\ 


FIG.  2-2. —  Isothermal  and  Adiabatic  Changes  Compared. 

The  various  fundamental  changes  which  may  take  place  in  a 
perfect  heat  engine  are  represented  by  the  diagram,  Fig.  2-2,  in 
which  0  V  is  the  base  line  from  which  pressures  are  measured  and 
0  P  the  zero  volume  line  from  which  volumes  are  measured.  In 
the  diagram  G  A  is  a  vertical  line  and  represents  the  condition  of 
receiving  heat  at  constant  volume;  A  B,  a  horizontal  line,  repre- 
sents the  condition  of  receiving  heat  at  constant  pressure ;  B  C, 
a  plain  hyperbola,  represents  isothermal  expansion,  and  B  D,  a 
logarithmic  curve,  represents  adiabatic  expansion;  D  E,  a  vertical 
line,  represents  the  discharge  of  heat  at  constant  volume;  E  F, 
a  horizontal  line,  represents  the  discharge  of  heat  at  constant 
pressure;  FG,  a  logarithmic  curve,  represents  adiabatic  compression, 
and  F  H,  a  plain  hyperbola,  represents  isothermal  compression. 
The  area  of  the  diagram,  ABDE  FG,  represents  the  external 
work  done  with  adiabatic  expansion  and  compression,  and  ABC 
E  F  H  A  represents  the  work  done  with  isothermal  expansion 
and  compression. 

During  the  period  of  receiving  'heat  at  constant  volume, 
represented  by  AG,  the  absolute  temperature  may  be  computed 


58 


INTERNAL  COMBUSTION   ENGINES 


at  A,  from  (12),  provided  it  is  known  at  G,  since  it  is  proportional 
to  the  pressures  at  those  points. 

During  the  period  of  receiving  heat  at  constant  pressure, 
represented  by  A  B,  the  absolute  temperature  increases  in  pro- 
portion to  the  volume,  as  shown  in  equation  (13),  and  if  known 
at  one  point  may  be  computed  at  any  other.  As  the  volume  is 
proportional  to  the  distance  from  the  line  0  P,  the  temperature 
on  the  line  A  B  will  be  proportional  to  that  distance. 

If  the  expansion  is  isothermal  the  temperature  would  remain 
constant  from  B  to  C.  If  the  expansion  is  adiabatic,  as  from  B 
to  D,  the  temperature  could  be  calculated  from  either  equation 
(16)  or  (17)  for  various  points  of  the  curve. 

The  actual  pressure- volume  diagram  as  taken  with  the  indicator 
shows  lines  which  only  approximate  those  for  constant  pressure, 
constant  temperature,  or  constant  volume  as  shown  in  Fig.  2-2.  The 
corners  of  actual  diagrams  are  likely  to  be  rounded  to  a  considerable 
extent  and  many  of  the  transformations  indicated  may  not  appear. 


100  ribs. 


0  0.0        0.1         0.2        0.3        0.4  cu.  £t. 

FIG.  2-3.  —  Four-cycle  Engine  Diagram. 


THERMODYNAMICS  OF  THE  GAS  ENGINE 


59 


Figure  2-3  represents  a  diagram  of  a  4-cycle  engine  in  which 
the  ordinates  have  been  enlarged  relatively  with  respect  to  the 
abscissae  and  on  which  there  have  been  drawn  a  line  of  no  volume, 
often  called  the  clearance  line,  and  a  line  of  zero  pressure.  The 
scale  of  ordinates  is  attached  to  the  diagram.  If  we  assume 
that  the  line  a  f  is  a  vertical  line  and  that  the  temperature  at 
the  lower  end  of  that  line  is  567  degrees  absolute,  then  we  find 
by  computation,  as  explained  above,  that  for  the  point  a  it  is 
1995  degrees  absolute.  As  absolute  temperature  F  is  460  degrees 
higher  than  that  shown  on  a  thermometer,  the  temperature  F 
at  these  two  points  would  correspond  to  107  degrees  and  1535 
degrees. 

The  heat  transformations  may  also  be  represented  by  the 
entropy  temperature  diagram,  in  which  case  the  ordinates  be- 
come temperature  and  entropy  instead  of  pressure  and  volume, 
p 


o  v 

FIG.  2-4.  —  Pressure  Volume  Diagram  of  Isothermal  and 
Adiabatic  Changes. 

A  simple  illustration  is  shown  in  Figs.  2-4  and  2-5.  In  Fig.  2-4 
is  shown  a  pressure-volume  diagram  of  a  working  material  which 
expands  isothermally  from  A  to  B,  then  adiabatically  from  B  to 
C.  It  is  then  compressed  isothermally  from  C  to  D  and  adiabati- 
cally from  D  to  A,  when  it  reaches  the  initial  condition.  The  me- 
chanical work  performed  during  these  operations  is  proportional 
to  the  area  of  the  diagram  A  B  C  D.  This  diagram  may  be 


60 


INTERNAL  COMBUSTION  ENGINES 


transformed  into  a  temperature  entropy  diagram  very  easily, 
since  for  that  case  the  isothermal  lines  A  B  and  B  C,  would  be 
horizontal  and  parallel  to  the  line  of  zero  temperature,  and  the 
adiabatic  lines  A  D  and  D  C  would  be  vertical  and  parallel  to  the 
line  from  which  entropy  is  reckoned.  Fig.  2-5  shows  the  tem- 
perature-entropy diagram 
constructed  as  described. 
The  area  of  this  diagram 
shows  the  heat  trans- 
ferred into  work.  For  the 
case  considered  this  is 
a  rectangle  and  its  area 
represents  the  maximum 
amount  of  heat  available 
for  work  within  the  tem- 
perature limits  A  B  and 
DC. 

The  case  considered  is 
that  of  the  perfect  rever- 
sible engine  which  operates 
~~^  in  a  Carnot  cycle,  as  al- 
FIG.  2-5.  —  Entropy-Temperature  Diagram.  ready  described.  It  appears 
from  the  diagram,  Fig.  2-5,  as  well  as  from  the  demonstration,  that 
an  engine  working  on  this  principle  can  transform  the  maximum 
amount  of  heat  into  work. 

An  engine  working  on  any  other 
principle,  as  for  instance  that  shown  in 
the  Fig.  2-2  A  B  D  E  F  G  A,  will  trans- 
form a  less  amount  of  heat  into  work. 
For  this  case  there  is  both  adiabatic 
expansion  B  D  and  adiabatic  com- 
pression F  G.  The  entropy-tempera- 
ture diagram  for  this  case  is  repre- 
sented, but  not  to  scale,  in  Fig.  2-6  by  the 
diagram  A  B  D  E  F  G,  which  by  in- 
spection is  smaller  and  shows  less  heat 
available  for  work  than  the  diagram  FIG.  2-6. 

m  B  n  F,  which  is  drawn  between  the  same  temperature  limits. 
For  the  figure  A  B  C  E  F  H,  shown  in  Fig.  2-2,  as  a  pressure- 


THERMODYNAMICS  OF  THE  GAS  ENGINE 


61 


volume  diagram  we  have  isothermal  expansion  B  C  and  isother- 
mal compression  F  H.  The  entropy-temperature  diagram  for 
this  case  is  represented  by  the  T 
diagram,  not  drawn  to  scale,  in 
Fig.  2-7,  A  B  C  E  FH,  which  by  in- 
spection is  smaller  and  shows  less 
heat  available  for  work  than  the 
diagram  m  C  n  H,  which  is  drawn 
between  the  same  temperature 
limit.  The  transformation  of  the 
pressure-volume  diagram  as  taken 
the  indicator  into  entropy- 


on 


FIG.  2-7. 


temperature  diagram  is  given  at  length  later  in  the  book. 

10.   Comparison   of  Theoretical    and   Actual  Heat  Engines. 

-  When  a  gas  after  a  series  of  transformations  of  pressure- 
volume  and  temperature  passes  through  a  series  of  intermediate 
states  and  of  physical  and  chemical  changes  and  returns  to 
the  same  condition,  in  all .  respects,  which  it  possessed  at 
the  beginning  of  the  transformations,  it  is  said  to  operate  in  a 
closed  cycle. 

It  is  evident  that  if  a  change  of  composition  occurs  during  the 
course  of  the  cycle  the  body  may  return  to  its  initial  condition  so 
far  as  pressure  and  volume  are  concerned  without  returning  to  its 
initial  condition  in  other  respects;  for  example,  a  mixture  com- 
posed of  hydrogen,  carbon  monoxide,  methane,  carbon  dioxide 
and  nitrogen,  with  which  the  cylinder  is  charged  in  the  initial 
condition  before  combustion,  may  be  changed  during  combustion 
to  the  vapor  of  water,  carbon  dioxide,  and  nitrogen,  which  change 
would  not  be  shown  on  the  indicator  diagram. 

In  the  actual  operation  of  the  internal  combustion  engine  the 
gas  or  vapor  is  subjected  to  periodical  changes,  as  outlined  above 
which  do  not  constitute  rigorously  closed  cycles.  The  operation 
is,  however,  approximately  a  closed  cycle  since  the  state  of  the 
working  fluid  after  each  series  of  changes  returns  to  its  initial 
state,  from  which  all  the  operations  as  to  chemical  and  physical 
changes  are  reproduced  as  in  the  preceding  phase. 

The  machine  in  which  the  changes  take  place  will  be  a  perfect 
neat  engine  if  all  of  the  heat  disappearing  has  been  transformed 
into  wrork;  it  has  been  demonstrated  practically,  however,  that  it 


62  INTERNAL  COMBUSTION  ENGINES 

is  not  possible  to  utilize  all  of  the  heat,  consequently  it  is  necessary 
to  expend  in  heat  a  larger  quantity  than  its  equivalent  in  units 
of  work.  It  has  already  been  shown  in  effect  that  it  is  not  only 
necessary  to  have  a  place  of  combustion  which  produces  a  high 
temperature  at  the  beginning  of  the  period  of  movement,  but  it  is 
also  necessary  to  have  a  point  of  lower  temperature  which  will 
act  as  a  refrigerator  and  permit  the  flow  of  heat  from  a  higher  to 
a  lower  temperature  level.  The  quantity  of  heat  Q  supplied  by 
the  combustion  less  the  amount  q  taken  up  by  the  refrigerator 
leaves  a  difference  Q  —  q  which  may  be  utilized.  From  this 
statement  it  would  appear  that  the  amount  of  work  possible 
would  be  increased  either  by  increasing  Q  or  by  diminishing  q. 
The  temperature  of  the  discharge  heat  q  must  evidently  be  con- 
siderably above  that  of  absolute  zero  because  of  the  difficulty  of 
obtaining  a  refrigerant  of  low  temperature  and  of  disposing  of 
the  heat  which  would  be  discharged  under  such  a  condition. 
Generally  in  practice  the  temperature  of  the  discharge  heat  is 
considerably  above  that  of  the  surrounding  air,  which  is  much 
in  excess  of  absolute  zero. 

The  ratio  of  Q  —  q  to  Q  measures  the  perfection  of  the  heat 
engine.  This  we  will  call  the  cyclic  efficiency 

— ~±  =  cyclic  efficiency 
v 

It  is  of  great  practical  interest  to  know  how  to  determine  the 
value  of  this  coefficient  for  any  case,  but  we  should  at  first  estab- 
lish the  maximum  value  that  can  be  obtained. 

In  this  connection  the  cycle  of  Carnot  which  is  formed  of  two 
isothermal  lines  and  two  adiabatic  lines,  Figs.  2—4  and  2—5,  should 
receive  consideration,  since  it  is  the  one  which  gives  the  maximum 
work  returned  for  the  heat  expended. 

The  Carnot  cycle  is  represented  in  the  pressure-volume  dia- 
gram Fig.  2-4,  in  which  a  mass  of  fluid  in  its  initial  state  p0v0,  with 
temperature  T0  as  shown  at  A,  expands  in  volume  isothermally  to 
B,  at  which  point  it  has  pressure  and  volume  p^.  From  B  it 
expands  to  C  without  gain  or  loss  of  heat,  following  the  adiabatic 
B  C.  From  C  to  D  there  is  a  discharge  of  heat  into  a  colder  body 
or  refrigerator  at  constant  temperature,  during  which  time  the 
volume  is  reduced  from  v2  to  ^3.  From  D  to  A  compression  takes 


THERMODYNAMICS  OF  THE  GAS  ENGINE  63 

place  without  gain  or  loss  of  heat,  which  raises  the  temperature 
to  that  of  the  initial  state  at  A. 

In  order  to  carry  out  the  cycle  of  operation  described,  sufficient 
heat  must  be  supplied  during  the  isothermal  expansion  from  A 
to  B  to  keep  the  temperature  constant;  this  amount  by  equation 

7) 

(19)  will  be  Q  =  A  R  T  log-1-.     In  the  adiabatic  expansion  from 

B  to  C,  during  which  there  is  neither  gain  nor  loss  of  heat,  the  rela- 
tions of  the  volumes  to  the  temperatures  are  expressed  by  equa- 
tion (16)  T  AM 

— 1  =(  _2 

T2     W 

During  the  third  period  from  C  to  D  heat  is  discharged  at  con- 
stant temperature  and  can  be  expressed  as  before  q  =  A  R  T  log 

-2.  During  the  fourth  period  the  quantity  of  heat  remains  con- 
stant and  we  have  >T  A,.  \v  l 

-to     fV»\y  —  i 


The  cycle  as  above  described  is  a  closed  one,  and  as  the  heat  re- 
ceived and  discharged  is  of  constant  temperature  it  follows  that 


The  work  produced  is  equal  to  the  area  A  B  C  D.     The  efficiency 
of  the  cycle  is  Q  —  q     T  —  T 

~Q~     ^TT 

This  is  equal  to  the  ratio  of  the  fall  of  temperature  to  the  absolute 
temperature  of  the  initial  condition. 

The  Carnot  cycle  may  also  be  represented,  as  already  shown, 
by  the  temperature-entropy  diagram,  in  which  case  the  diagram 
will  be  a  rectangle,  Fig.  2-5. 

It  is  doubtless  true  that  no  better  method  exists  for  utilizing 
the  heat  furnished  by  combustion  than  that  of  supplying  it  at  con- 
stant temperature,  permitting  the  body  to  expand  without  gain  or 
loss  of  heat,  discharging  it  to  the  refrigerator  at  a  constant  tem- 
perature, which  should  be  as  low  as  possible,  and  compressing 
without  gain  or  loss  of  heat  to  the  original  temperature. 

Theoretically  it  is  possible  to  equal  but  not  to  surpass  the 
return  from  the  Carnot  cycle.  The  maximum  effect  that  can  be 


64  INTERNAL  COMBUSTION  ENGINES 

obtained  from  a  heat  engine  working  between  the  temperatures 
T  and  Tf,  and  in  which  Q  is  the  heat  expended,  is  expressed  by  the 
equation  , 


In  order  to  judge  the  theoretical  value  of  a  cycle  on  which  any 
heat  engine  operates  it  is  desirable  to  calculate  at  first  the  coefficient 
of  economy  of  the  proposed  cycle,  then  compare  this  coefficient 
with  the  Carnot  coefficient  between  the  same  temperature  limits. 

The  knowledge  which  is  given  by  comparing  the  cycle  of  the 
engine  with  the  Carnot  cycle  is  not  sufficient  to  determine  the 
practical  value  of  the  engine,  since  the  effect  of  friction,  shocks 
due  to  inertia,  and  the  passive  resistance  of  the  various  mechanical 
parts  consume  a  portion  of  the  work  supplied  by  the  transfor- 
mation of  heat  and  do  not  appear  in  the  useful  work  delivered  by 
the  machine.  It  is  quite  possible  that  machines  which  have  a 
high  degree  of  perfection  for  the  transformation  of  heat  will  still 
give  small  return  as  practical,  useful  machines. 

The  hot-air  engines  for  example,  which  have  a  perfect  cycle 
of  operation,  have  proved  in  practice  of  little  value  because  of 
the  small  amount  of  heat  that  would  pass  through  a  metallic  wall 
in  a  given  time,  and  as  a  consequence  the  return  in  useful  work 
is  small  in  proportion  to  the  expense  of  construction.  There  are 
few  engines  of  any  kind  which  operate  in  a  cycle  approximat- 
ing that  of  Carnot,  among  these  should  be  mentioned  the  Sterling 
air  engine,  which  theoretically  operates  on  the  Carnot  cycle. 

The  cycle  of  operation  of  the  steam  engine  is  incomplete  in 
many  respects;  it  however  resembles  that  of  Carnot  in  that  heat 
is  received  into  the  engine  cylinder,  until  the  valve  closes  connec- 
tion with  the  boiler,  at  practically  constant  temperature.  After 
cut-off  the  steam  is  expanded  approximately  without  gain  or  loss 
of  heat.  It  is  then  discharged  through  the  condenser  at  constant 
temperature.  The  adiabatic  compression  is  sometimes  considered 
as  being  performed  by  the  feed  pump  which  supplies  water  to  the 
boiler.  The  steam  engine  cycle  is  thus  seen,  when  the  boiler 
furnace  and  boiler  feed  pump  are  included  as  a  part,  to  approxi- 
mate that  of  the  Carnot  cycle. 

The  Diesel  motor  is  the  only  gas  engine  which  approximates 
in  the  theory  of  its  operation  to  the  Carnot  cycle. 


CHAPTER   III 

THEORETICAL    COMPARISON    OF    VARIOUS    TYPES    OF    INTERNAL 
COMBUSTION    ENGINES 

1.  Throughout    the   following    discussion   of   the   theoretical 
cycles  it  will  be  assumed  that  the  specific  heats  at  constant  volume 
Cv,  and  at  constant  pressure  Cp,  do  not  vary  either  with  pressure 
or  temperature.     It  has  been  shown  that  they  vary,  but  the 
question  is  unsettled.     If  the  variation  is  such  as  determined  by 
the  experiments  of  Mallard  and  Le  Chatelier,  which  are  extensively 
quoted,  our  present-day  gas    engine  does  not  admit  thermally 
of  any  further    improvement.       In  view  of  this  unsettled  con- 
dition  it    is   best   to    assume   the   specific    heats    constant.      It 
is  further  assumed,  in  this  theoretical  discussion,  that  the  value 

C1 

of  y  =  -^  is  the  same  for  the  burned  gases  as  for  the  fresh  fuel 

C7; 

mixture. 

It  is  further  understood  that,  wherever  heat  supplied  to  a  cycle 
is  mentioned,  it  refers  to  the  lower  heating  value  of  the  fuel  con- 
cerned, either  per  pound  or  per  standard  cubic  foot,  as  stated. 

2.  The   cycle  receiving  heat   at  constant  volume,  Beau  de 
Rochas  or  Otto  cycle. 

The  principles  upon  which  the  present-day  constant  volume 
combustion  engine  is  based,  and  which  helped  it  to  its  commercial 
success,  were  first  clearly  enunciated  by  Beau  de  Rochas  in  a 
written  pamphlet  in  1862.  It  remained  for  Otto,  however,  to 
construct  the  first  practically  successful  machine  operating  with 
this  cycle,  hence  the  cycle  receiving  heat  at  constant  volume  is 
more  often  known  as  the  Otto  cycle. 

In  what  follows  let 

Q  =  quantity  of  heat  received  by  the  theoretical  cycle, 

q  =  quantity  of  heat  rejected  by  the  theoretical  cycle, 

then    Ec  =  the    cycle    efficiency  =  -^--. 

65 


66 


INTERNAL  COMBUSTION  ENGINES 


It  shows  the  highest  efficiency  which  an  engine  could  possibly 
show  if  it  could  follow  exactly  the  lines  of  the  theoretical  cycle. 
Practically  this  can  never  be  realized,  but  the  conditions  which 
determine  why  the  actual  thermal  efficiency  of  an  engine  is  always 
less  than  the  cyclic  efficiency  will  be  treated  in  detail  later  on. 

In  Fig.  3-1,  at  the  end  of  the  charging  stroke,  whether  that  be 
in  the  two-  or  in  the  four-cycle,  the  charge  is  under  a  pressure, 
temperature,  and  volume  determined  by  the  point  1.  Adiabatic 
compression  then  takes  place  to  2.  A  quantity  of  heat,  Q,  is 
next  received  at  constant  volume  to  3.  From  3  to  4  adiabatic 
expansion  takes  place,  and  finally  the  quantity  of  heat,  q,  is  re- 
jected along  line  4-1  at  constant  volume. 

1       3, 


FIG  3-1. 


Let  the  total  charge  weight  be  G  Ibs.  This  consists  of  Ga 
Ibs.  air,  Gg  Ibs.  gaseous  fuel,  and  Gr  Ibs.  burned  gases  from  the 
previous  cycle. 

a) 

(2) 


Q  =  GC,  (T,  -  T,) 
q  ==  GCV  (T,  -  T,) 
Hence  the  heat  utilized  by  the  cycle  is 

'  Q  -  q  =  GCV  (T,  -  T2  -  Tt  +  T 
and  the  cyclic  efficiency 

E   _Q-V=GCv(T3-T2-T4+TJ 


(3) 

(4) 
(5) 


Tt-T, 


THEORETICAL   CYCLES  67 

Again,  in  Fig.  3-1,  let  vc  =  clearance  volume,  and  vs  =  stroke 
volume,  so  that  vt  =  vc  +  v  s  =  total  volume.  We  may  write, 
since  compression  and  expansion  are  assumed  adiabatic, 


(6) 
and 

P^l  =  P*$-  (7) 

Dividing  (6)  by  (7),  ^  =  ^.  (8) 

Ps     P* 


Now      2=? 

T3    p3  4     p, 

hence  finally  ^  =  J  or  ^  =  ^  (9) 

^3        ^4  ^3.       ^2 

With  the  aid  of  (9),  equation  (5)  may  be  written 

S)      | 

(10) 

There  are  two  other  ways  of  stating  the  cyclic  efficiency  which 
will  be  developed  next. 
Again  we  can  write 

PiV=P2^Y  (11) 

also  , 

f\ 


Dividing  (11)  by  (12)  v 

1  v-l  A 


or 

Y— i 


aV'V         "V-1  (13) 

in  which  r  =  the  compression  ratio  —  . 
Hence 

B'=1~fi~1~7?=I  (14) 


68  INTERNAL  COMBUSTION   ENGINES 

Finally,  raise  equation  (12)  to  the  y  power 

y   y  y     y 

Pi    Vt      =  P-2   Vc  (15) 


and  divide  (11)  by  (15).     We  shall  have 

y-l 


from  which  —1 

E«=l_j!=l_(P«)   y  (17) 

1  2  F2 

From  an  examination  .of  equations  (14)  and  (17)  it  will  be  seen 

C 

that  Ec  depends  upon  r  or  p2,  and  y  =  ~. 

Lv 

To  make  clear  the  influence  of  the  value  of  y,  assume  that  in 
two  given  cases  the  value  of  r  =  5,  but  that  in  the  first  case  a 
rich  gas  mixture  with  y=  1.35,  in  the  second  case  a  lean  gas  mixture 
with  y  =  1.39  be  employed.  Then  for  the  two  cases  we  shall  have 

^1-T~5-431 

and  Ec=l-~~=A6Q 

(&) 

The  advantage  in  favor  of  the  lean  gas  mixture  is  therefore 
.466-.  431  _ 

-431" 

Besides  this  the  use  of  lean  gas  mixtures  in  practice  usually 
shows  a  smaller  jacket  water  loss,  owing  to  the  lower  mean  tem- 
perature of  the  entire  cycle. 

The  value  of  Ec  also  depends  upon  the  ratio  &,  according  to 

?72 

eq.  (17).  The  smaller  this  ratio  the  greater  the  efficiency.  But 
the  value  of  plt  the  suction  pressure,  is  almost  entirely  out  of  our 
control,  so  that  the  problem  narrows  down  to  making  p2,  the  com- 
pression pressure,  as  high  as  possible.  This  brings  out  clearly 
the  value  of  high  compression.  The  practical  limits  to  this  state- 
ment will  be  pointed  out  later  on. 

To  show  the  combined  influence  upon  Ec  of  r  or  p2  and  y  the 
following  table,  from  Giildner,  is  given: 


THEORETICAL   CYCLES  69 

CYCLIC  EFFICIENCIES,  Ec.,  FOR  THE  OTTO  CYCLE 


r  = 

2.0 

2.5 

3.0 

3.5 

4.0 

4.5 

5.0 

6.0 

7.0 

8.0 

9.0 

10.0 

y  =  1.20 

.129 

.167 

.197 

.221 

.242 

.260 

.275 

.301 

.322 

.340 

.356 

.361 

=  1.25 

.159 

.205 

.240 

.269 

.290 

.313 

.331 

.361 

.385 

.405 

.423 

.438 

1.30 

.188 

.241 

.281 

.313 

.343 

.363 

.383 

.416 

.442 

.464 

.483 

.499 

1.35 

.216 

.274 

.319 

.355 

.384 

.409 

.431 

.466 

.494 

.517 

.537 

.553 

1.40 

.248 

.313 

.363 

.402 

.434 

.460 

.483 

.520 

.550 

.574 

.594 

.611 

3.    The   cycle    receiving   heat   at    a   constant    pressure,   the 
Bray  ton  cycle,  and  the  approximate  Diesel  cycle  of  to-day. 

The  Brayton  Cycle. 

In  the  older  machines  of  the  Brayton  type,  suction  and  com- 
pression of  the  fuel  mixture  or  of  air  took  place  in  one  cylinder, 


a  i 


FIG.  3-2. 

while  the  combustion,  expansion,  and  exhaust  took  place  in 
another.  In  Fig.  3-2,  area  b  1  2  a  b  represents  the  pump  diagram, 
area  a  3  4  b  a  the  diagram  from  the  power  cylinder.  For  the 
purpose  of  theoretical  discussion  of  this  cycle,  the  two  diagrams 
may  be  combined  as  shown,  giving  in  area  1234  the  useful  work 
developed. 

The  compression  line,  1-2,  and  the  expansion  line,  3-4,  are 
again  assumed  adiabatic.  Expansion  is  carried  to  exhaust 
pressure.  The  quantity  of  heat  Q  is  received  along  2-3,  the 
amount  q  is  rejected  along  4-1,  at  constant  pressure  in  both 
cases. 


70  INTERNAL  COMBUSTION  ENGINES 

Let  the  charge  weight  be  G  pounds  made  up  as  in  the  pre- 
vious ease.     Then 

Q  =  GCp(T3  -  rjB.T.U. 
and 

q  =  GCp  (T,  -  7\)  B.  T.  U. 

Her  E_Q~q_ 

~ 


GCP(T3-T2) 
_l     T4-T,  (18) 

But  from  the  adiabatic  law  we  may  write 

(19) 


and 

(20) 


Divide  (19)  by  (20), 

/t>AY    /uAY 

or 


(21) 


Also, 

J^L  _  PjP±     or  since  p*  =  p4,    —  =  ^  (22) 

rtl  FJ~1  '  1    A          i    »/        rry  fT\  ^          / 

*•  1  •*•   4  ^1^4 

and  similarly 

^=^3  (23) 

From  (22) 

~  =  Y  (24) 

From  (23) 

5=ft  (25) 

Equations  (25)  and  (24)  in  combination  with  (21)  finally  give 

rr\          rp      ^**-    rp          rn 

Substituting  (26)  in  (18),  we  have 

T  T  * 

J7i  1         Jl_1         J4  /Q7\ 

&c—  l  —  -nr—l  —  fjr  (21) 


THEORETICAL   CYCLES 


71 


But  it  has  already  been  shown,  equation  (13),  that  for  adiabatic 
compression 


so  that  finally  the  cyclic  efficiency  for  combustion  at  constant 
pressure  is  .. 

Ec=l~r-^r  V          <28> 

which  is  the  same  as  for  combustion  at  constant  volume. 

The  Diesel  Cycle  of  to-day. 

The  Diesel  cycle  of  to-day  approximates  the  constant-pressure 
form  outlined  in  Fig.  3-3.     Compression  line  1-2  and  expansion 


j. 


FIG.  3-3. 

line  3-4  are  assumed  adiabatic.  Heat  is  received  at  constant 
pressure  along  line  2-3,  and  rejected  at  constant  volume  along 
line  4-1.  In  the  Otto  cycle,  with  the  machine  at  full  load,  the 
ratio  of  compression  is  equal  to  the  ratio  of  expansion.  In  the 

Diesel,  the  ratio  of  compression  — ,  (see  Fig.  3-3), is  always  greater 

V  c 

than  the  ration  of  expansion,  — . 

Ve 

Let  the  charge  weight  again  be  G  pounds.  Diesel  machines,  as 
constructed,  are  oil  engines,  so  that  the  increase  of  charge  weight 
along  line  2-3  is  small  and  'may  be  neglected  without  serious 
error.  That  is,  we  may  assume  G  constant  for  the  cycle.  If  the 
investigation,  however,  is  carried  through  for  a  gas,  especially  a 
lean  gas,  this  assumption  is  not  permissible. 


72  INTERNAL  COMBUSTION    ENGINES 

To  develop  the  efficiency  formula,  we  may  write 

Q  -  GCp  (Ta  -  T2).  (29) 

q   ^GC^Tt-TJ.  (30) 

Now  from  Fig.  3—3 

£  &    ««   T"*   '7^       ^ '7~'    ^  ^Q 1  ^ 

/TI  /T7  3  2  ..  2  \        / 

j.   2  3  ^ 

where,  8  =  ratio  of  cut-off  volume  to  clearance  volume. 

Also 

Pf  =  |l  from  which  T4=T^  (32) 

But  from  the  adiabatic  law 

p4  v4v  =  p3  vs  >  from  which  p4= 

and 

^9,7?^  =  p2v2"*  from  which  pt  =  — 

Hence  (32)  may  be  written 


Substituting  (31)  and  (33)  in  (29)  and  (30)  respectively, 
Q  =  GCPT2  (8-1). 
q  =GCVTV  (8V-1). 
The  cyclic  efficiency  for  the  Diesel  cycle  consequently  is 

_  Q-g  _  q  _  GCyg\(y-l) 

- 


71         1 
But  it  has  shown,  equation  (13),  that  -^  =  =    y.Y_1 


.. 

fuNlVERSlTY 

^V  ^ 

THEORETICAL   CYCLES  73 

hence  finally 


l)  (34) 

Equation  (34)  shows  that  the  expression  for  the  theoretical 
efficiency  of  the  Diesel  cycle  is  the  same  as  that  for  the  Otto  and 

87-l 

the  Brayton,  with  the  exception  of  the  factor—^ — --  .  The  effi- 
ciency thus  depends  not  only  upon  r  and  y,  but  also  upon  8,  that 
is,  finally,  on  the  volume  at  cut-off. 

In  actual  practice  the  cut-off  volume  ve  is  about  10  per  cent 
of  the  stroke  at  full  load.  With  a  compression  ratio  of  r  =  13, 
this  makes  8  about  =  2.5.  To  show  the  influence  of  the  factor 
8  upon  Ec,  assume  y  =  1.35.  The  efficiencies  for  full  load,  8  = 
2.5,  an  overload,  8  =  3.0,  and  some  partial  load,  8  =  1.5,  will  be 
as  follows: 

Cyclic  Efficiency  Ec  for  the  Diesel  cycle. 

For  8  =  Ve.  =  1.5         2.5         3.0 

vc 
and  for  r  =  13,  and   y  «  1.35,  Ec  =    .560       .509       .487. 

It  appears  from  this  that,  other  conditions  remaining  the 
same,  the  smaller  the  value  of  8,  the  greater  Ec.  This  result  is 
actually  borne  out  in  practice,  within  limits,  where  a  large  num- 
ber of  tests  of  Diessl  engines  have  often  shown  a  greater  thermal 
efficiency  at  three-quarters  than  at  full  load.  That  this  condition 
does  not  hold  for  still  lower  loads  is  due  to  other  circumstances. 

4.   Comparison  of  Various  Cycles. 

The  question  of  the  best  gas-engine  cycle  has  often  been  dis- 
cussed. In  general,  there  is  no  best  gas-engine  cycle,  but  that 
cycle  should  be  chosen  which  will  give  the  best  return  for  the 
practical  conditions  existing. 

To  give  some  insight  into  the  problem  of  choosing  the  cycle 
best  adapted  to  given  conditions,  we  will  first  obtain  some  theo- 
retical basis  of  comparison,  and  show  afterwards  how  this  is 
affected  in  practice. 

Many  methods  of  comparison  have  been  employed  by  various 
writers,  but  the  following,  due  originally  to  E.  Meyer  *  seems  to 
the  writer  to  be  the  clearest  and  most  comprehensive. 

*Zeitschrift  des  Vereins  deutscher  Ingcnieure,  1897,  p-.  1108, 


74 


INTERNAL  COMBUSTION  ENGINES 


Using  the  Carnot  cycle  as  a  basis  of  comparison,  it  is  clear 
that  the  amount  of  heat  transferred  into  mechanical  work  de- 
pends only  upon  the  total  amount  of  heat  and  the  temperature 
difference  in  the  cycle.  But  to  become  available  as  a  basis  for 
the  comparison  of  gas-engine  cycles,  only  that  Carnot  cycle  can 
be  used  for  which  the  heat  element  8^,  supplied  at  a  constant 
temperature  7\,  and  the  heat  element  8g2  rejected  at  a  constant 
temperature  T2,  are  of  infinitesimal  amount,  so  that  the  two 
adiabatics  forming  the  rest  of  the  cycle  are  infinitely  close  to- 
gether. Then  every  closed  cycle  may,  by  a  number  of  adiabatics, 
be  divided  into  an  infinite  number  of  elementary  cycles,  Fig.  3-4, 


FIG.  3-4. 

for  each  of  which  we  may  with  very  small  error  assume  that  the 
heat  element  8^  is  supplied  at  a  constant  temperature  Tlf  and  the 
heat  element  8<?2  is  rejected  at  the  constant  temperature  T2.  The 
efficiency  of  one  of  these  elementary  Carnot  cycles  may  be  ex- 
pressed for  say  the  nth  cycle  by 


From  the  above  equation  we  at  once  derive  the  important 
requirement  that  for  best  efficiency  each  heat  element  8^  should 
be  supplied  to  the  working  fluid  at  the  highest  temperature  pos- 
sible, and  each  element  S#2,  should  be  rejected  at  the  lowest 
possible  temperature,  that  is,  the  temperature  limits  should  be 
as  wide  as  possible. 

It  should  be  observed,  however,  that  the  above  requirement 


THEORETICAL   CYCLES 


75 


does  not  mean  that  the  sum  total  of  all  the  heat  elements  8gt 
must  be  supplied  isothermally,  or  that  the  sum  total  of  the  ele- 
ments 8#2  rejected  must  be  taken  up  isothermally.  For  in  general 
in  gas.  engines  the  various  successive  heat  elements  are  not  avail- 
able at  constant  temperature,  and  in  fact  in  following  out  the 
requirement  above  outlined  for  best  efficiency,  one  would  be 
led  to  constantly  change  the  temperature  of  supply  and  of  rejec- 
tion to  widen  the  temperature  limits  as  far  as  possible.  It  is 
clear,  therefore,  that  only  in  the  case  where  all  the  heat  elements 
supplied  are  available  at  constant  temperature,  and  all  those 
rejected  can  be  taken  up  at  constant  temperature,  as  is  the  case 
in  a  steam  engine,  will  the  Carnot  cycle  represent  the  ideal. 

Now  consider  one  of  the  elementary  Carnot  cycles,  into  which 
the  gas-engine  cycle  has  been  divided,  by  itself,  Fig.  3-5. 


FIG.  3-5. 


For  the  point  1  we  may  write 


R 

and  since  during  the  supply  of  the  infinitesimal  heat  element  Sg, 
the  values  of  pl  and  ^  increase  only  by  infinitesimal  amounts,  we 
may  assume  without  great  error  that  the  volume  and  pressure  at 
the  end  of  the  heat  supply  are  also  represented  by  vl  and  pt 
respectively.  Similarly  we  may  write  for  the  point  2 


T9= 


R 


The  efficiency  of  the  elementary  cycle  under  discussion  is  then 


76  INTERNAL  COMBUSTION   ENGINES 

But  since  the  other  enclosing  lines  are  adiabatics,  we  have 
Pivi  =  P-ivv  from  which 


Finally,  therefore,  y_1 

VT  (35) 

W 
In  connection  with  the  last  equation  it  should  be  observed 

T  —T 

that  while  the  expression  Ec  =    -±= — -  is  based  upon  the  general 

laws  of  thermodynamics,  and  is  therefore  applicable  to  all  work- 
ing fluids  without  exception,  equation  (35)  has  been  derived  from 

this    by    the    use   of  equations^-  ••  =  R,    and    pvy=  constant. 

Equation  (35)  is  therefore  strictly  applicable  to  gas  only. 

Equation  (35)  leads  to  the  following  important  deduction: 
To  obtain  the  best  efficiency  in  a  closed  cycle,  it  is  necessary  to  supply 
each  heat  element  at  such  a  pressure  p1  and  to  refect  the  part  not 

transformed  into  work  at  such  a  pressure  p2,  that  the  ratio  —  shall  be 

Pi 
as  large  as  possible. 

As  previously  pointed  out,  however,  in  the  case  of  the  gas 
engine,  the  pressure  p2  cannot  well  be  below  atmosphere  because 
the  use  of  a  vacuum  is  neither  practicable  nor  economical.  Hence 
the  meaning  of  equation  (35)  narrows  down  to  the  requirement 
to  introduce  each  heat  element  at  highest  possible  pressure  pt,  and  to 
reject  the  part  not  used  at  a  pressure  as  close  to  atmosphere  as  possible. 

With  this  knowledge  it  becomes  easy  to  compare  the  various  gas- 
engine  cycles  among  themselves  to  determine  which  of  the  pressure 
lines  at  which  heat  is  supplied  gives  the  best  guarantee  of  efficiency. 

Figure  3-6  represents  the  cycle  with  combustion  at  constant 
volume,  Fig.  3-7  the  constant  pressure  cycle,  and  Fig.  3-8  the  cycle 
with  isothermal  combustion.  The  heat  is  rejected  in  each  case 
along  a  constant-pressure  line  as  nearly  as  possible  to  atmosphere. 
It  is  assumed  also  in  each  case  that  the  pressure  and  temperature 
at  the  end  of  compression  shall  be  the  same,  that  is,  that  pc  and 
Tf  in  Fig.  3-6  shall  be  equal  to  pf  and  Tc  in  Fig.  3-7,  etc, 


THEORETICAL   CYCLES 


77 


FIG.  3-6. 


FIG.  3-7. 


FIG.   3-8. 


78  INTERNAL  COMBUSTION  ENGINES 

Now  assume  that  each  cycle  is  divided  by  adiabatics  into  an 
infinite  number  of  elementary  cycles.  For  convenience  only  three 
of  these  are  indicated  in  each  figure.  With  combustion  at  constant 
volume  Fig.  3-6,  each  heat  element,  Sg/,  Sg/',  etc.,  supplied 
serves  to  raise  the  temperature  and  especially  the  pressure  for 
the  one  succeeding  it,  and  since  expansion  is  carried  to  atmosphere 
in  each  case,  it  is  plain  that  this  method  of  combustion  tends  of 
itself  to  fulfil  the  requirement  above  outlined.  On  account  of 
the  increasing  pressure  ranges,  the  efficiency  of  each  elementary 
cycle  is  in  this  case  greater  than  that  of  the  one  just  preced- 
ing it. 

The  same  course  of  reasoning  applied  to  combustion  at  con- 
stant pressure,  Fig.  3-7,  will  show  that  each  heat  element,  S<//, 
Sg/',  etc.,  while  it  serves  to  raise  the  temperature  does  not  raise 
the  pressure  for  the  next  succeeding  element.  The  expansion 
being  again  in  each  case  to  atmosphere,  the  pressure  ranges  for 
all  the  elementary  cycles,  and  hence  also  the  efficiency,  is  the 
same. 

The  case  of  combustion  at  constant  temperature,  Fig.  3-8,  is 
even  less  favorable.  Here  each  heat  element,  8g/,  Sg/',  etc., 
does  not  raise  the  temperature  for  the  succeeding  element,  but  is 
accompanied  by  a  decrease  of  pressure.  The  exhaust  pressure 
being  unchanged,  this  means  a  smaller  pressure  range  for  each 
succeeding  elementary  cycle,  and  consequently  a  steadily  decreas- 
ing efficiency. 

Looking  next  at  the  heat  discharged  from  each  elementary 
cycle,  we  may  write: 

Sg,/s-d&'-Aga' 
V  >  V'  >  V 

dq2'  =  dq2"  =  dq2f" 
Ag/<  Ag/<  Ag/" 

From  all  this  it  follows  that,  starting  with  the  same  pressure 
of  compression,  the  constant-volume  combustion  is  more  efficient 
than  that  at  constant  pressure;  and  this  in  turn  is  more  efficient 
than  isothermal  combustion. 

Isothermal  combustion,  being  so  obviously  inferior  to  the 
other  two  in  theory,  is  also  difficult  to  carry  into  operation  prac- 
tically, and  for  these  reasons  is  practically  obsolete. 


THEORETICAL   CYCLES 


79 


5.  Practical  conditions  affecting  the  choice  of  best  cycle  for 
any  given  case. 

It  is  evident  from  the  preceding  article  that  the  most  impor- 
tant item  in  the  efficiency  question  is  the  pressure  at  the  end  of 
compression.  The  aim  should  be  to  use  as  high  a  pressure  as 
possible  in  order  to  introduce  the  first  heat  element  at  the  highest 
possible  efficiency.  But  the  compression  pressure  governs  the 
maximum  pressure  and  temperature  occurring  in  the  cycle,  and 
that  brings  us  to  a  consideration  of  the  pressure  and  temperature 
limits. 

Of  these  two  the  temperature  limit  plays  but  a  secondary 
part,  because  it  is  possible  to  operate  on  a  cycle  whose  maximum 
temperature  may  be  3000  degrees  Fahrenheit  for  the  reason  that 


FIG.  3-9. 

these  maximum  temperatures  exist  but  for  a  very  short  time. 
The  pressure,  limit  is  more  important,  because  no  matter  how 
short  a  time  the  maximum  pressure  lasts,  the  driving  mechanism 
of  the  machine  must  be  built  for  this  pressure.  In  modern  prac- 
tice 550-600  pounds  seems  to  be  about  the  maximum  pressure 
limit  that  can  be  economically  handled.  Herein  we  find  a  condi- 
tion which  may  modify  the  conclusion  arrived  at  in  the  previous 
article  as  regards  comparative  efficiency  of  combustion  at  con- 
stant volume  and  at  constant  pressure. 

Assuming  the  more  practical  condition,  that  the  maximum 
pressures  in  the  two  cycles,  instead  of  the  compression  pressures, 
shall  be  the  same,  the  diagrams  would  be  placed  as  shown  in 
Fig.  3-9,  in  which  the  broken  line  represents  the  Otto  cycle.  It 
is  evident  in  such  a  case  that  only  the  last  heat  element  of  the 


80  INTERNAL  COMBUSTION  ENGINES 

Otto  cycle  is  introduced  at  the  same  efficiency  as  the  first,  and 
consequently  all,  of  the  heat  elements  of  the  cycle  at  constant 
volume.  Hence,  upon  these  premises,  the  constant-pressure 
cycle  is  more  efficient  than  the  constant  volume  cycle.  Under 
some  conditions,  however,  favorable  to  the  Otto  cycle,  this  advan- 
tage of  the  constant-pressure  cycle  is  not  very  great.  Thus  in  a 
Diesel  engine  cutting  off  at  full  load  at  10  per  cent,  8  =  2.5,  assume 
r  =  13,  and  y  =  1.41,  then  Ec  will  be  .564.  An  Otto  engine 
cycle  of  the  same  maximum  pressure  limit,  =  about  460  pounds, 
would  show  a  compression  pressure  of  from  190-225  pounds,  r 
would  be  about  equal  to  7,  and  with  y  =  1.41,  Ec  would  be  .550. 
This  shows  a  gain  for  the  Diesel  engine  of  only  1.5  per  cent,  but 
it  should  be  pointed  out  that  a  compression  pressure  of  200 
pounds  in  an  Otto  cycle  can  only  be  reached  with  extremely  lean 
fuel  gases,  or  with  separate  fuel  and  air  compression.  However 
that  may  be,  the  advantage  of  the  constant-pressure  cycle  over 
the  constant-volume  cycle,  presupposing  equal  maximum  pres- 
sures in  each,  is  comparatively  small,  and  hence  the  undoubted 
gain  that  the  Diesel  engine  shows  in  practice  over  the  average 
constant-volume  engine  is  by  some  writers  attributed  not  so 
much  to  the  cycle  as  to  the  greater  perfection  of  combustion. 
That  this  is  approximately  true  has  been  proven  by  Giildner  who 
constructed  engines  operating  on  the  Otto  cycle  upon  the  most 
advanced  ideas,  and  obtained  efficiencies  fully  as  good  as  those 
obtained  by  Diesel. 

A  second  limit  set  to  the  compression  pressure  that  can  be 
carried  is  due  to  pre-ignition.  All  fuel  mixtures  will  ignite  spon- 
taneously if  the  temperature  becomes  high  enough,  but  the 
critical  temperature  varies  greatly  for  the  different  fuels.  This 
fact  directly  governs  the  compression  pressure.  While  it  is  hardly 
advisable  to  use  more  than  say  80-90  pounds  in  the  case  of  a 
gasoline  mixture,  a  blast  furnace  gas  mixture  will  easily  stand 
150  pounds  without  pre-ignition.  Since  the  efficiency  of  the 
cycle  depends  directly  upon  the  compression  pressure,  as  above 
shown,  we  should  expect  a  better  efficiency  for  blast  furnace 
gas  than  for  gasoline,  and  this  is  actually  so  in  practice.  The 
difference,  however,  is  due  to  the  nature  of  the  fuel.  A  remedy 
for  this  state  of  affairs  would  be  to  compress  the  air  separately 
and  introduce  the  gasoline  or  other  fuel  oil  only  at  the  moment 


THEORETICAL   CYCLES  81 

combustion  is  desired.  This  leads  to  the  constant-pressure 
cycle,  and  thus  the  fuel  to  be  employed  should  be  considered  in 
the  choice  of  cycle. 

A  final  point  to  be  considered  is  this:  By  theory,  the  greater 
the  compression  pressure,  the  higher  the  efficiency.  This  holds 
for  either  type  of  cycle.  But  how  far  can  this  compression  be 
carried,  outside  of  the  questions  of  upper  pressure  limit  and  pre- 
ignition  above  considered,  before  the  added  gain  due  to  higher 
compression  is  in  practice  balanced  or  overbalanced  by  attendant 
losses. 

The  following  discussion  of  this  question  by  Giildner,  as  applied 
to  combustion  at  constant  volume,  is  instructive. 

The  efficiency  of  any  engine  should  not  be  judged  upon  cylin- 
der performance,  but  upon  the  performance  at  the  shaft.  Usually 
this  is  called  the  "  thermal  efficiency  per  brake  horse-power," 
but  a  shorter  and  more  expressive  term  which  the  authors  prefer 
and  will  use  in  this  treatise,  is  "  Economic  Efficiency  Ee." 

Now 

E.  =  E,Em  =  XEcEm. 
where 

Et  =  thermal  efficiency  per  indicated  horse-power. 

™  u  '    •    i-    m  •  r         •  Brake  H.  P. 

Em  =  mechanical  efficiency  of  engine  =          -  — 

Ec  =  cyclic  efficiency  as  derived  in  the  preceding  articles  = 

=  1  ---  -  for  combustion  at  constant  volume. 
7-1 
r 

and 

X    =  a  factor  such  that  Et  =  XEC,  so  that  X  is  always  less 
than  1. 

The  mechanical  efficiency  may  be  expressed  by 


Pi 
where 

Pf  =  mean  indicated  pressure  per  square  inch  of  piston, 
and 

PI  =  pressure  lost  in  friction  per  square  inch  of  piston. 


82  INTERNAL  COMBUSTION  ENGINES 

Hence 

Pi  -  Pf 


Pi 

The  value  of  Ee  therefore  depends  upon  the  relation  between 
the  factors  X,  pi}  and  pf,  as  modified  by  a  variation  in  r,  that 
is,  in  the  pressure  of  compression.  The  change  in  the  value  of 
X  due  to  a  variation  in  r  is  quite  unknown,  and  is  in  any  case 
so  small  that  it  may  be  neglected.  Regarding  the  relation 
between  p{,  p{,  and  r,  numerous  tests  have  shown  that,  as  r 

increases,  the  mechanical  efficiency  ^  y ,  is  at  first  quite  con- 
stant, but  that  after  a  certain  point  it  commences  to  decrease 
quite  rapidly.  This  is  due  to  the  fact  that  for  the  first  part  of 
the  range  any  increase  in  pf,  due  to  an  increase  in  r,  is  counter- 
balanced by  a  corresponding  gain  in  p^  Beyond  a  certain  point, 
however,  there  is  a  loss  in  p.,  owing  to  the  fact  that  the  fuel 
mixture  has  to  be  made  more  and  more  lean  to  prevent 
pre-ignition,  and  the  mechanical  efficiency  consequently  ^de- 
creases. Hence  we  have  the  net  result  that  as  long  as  an  increase 
in  p},  due  to  an  increase  in  r,  is  met  by  a  proportionate  gain 
in  pi,  the  Economic  Efficiency  Ee  will  increase.  Just  as  soon,  how- 
ever, as,  with  increase  in  r,  the  gain  in  pi  is  no  longer  sufficient  to 
overcome  the  increase  in  p/,  Ee  will  commence  to  decrease,  and  the 
economic  compression  limit  will  have  been  passed. 

Tests  and  computations  have  shown  that  up  to  r  =  6,  which 
means  a  compression  pressure  of  about  160  pounds,  the  mechani- 
cal efficiency  does  not  change  materially,  but  that  beyond  this  it 
commences  to  decrease.  This  is  probably  due  to  the  necessary 
increase  in  the  size  of  machine  parts  due  to  the  greater  pressures 
and  to  the  fact  that  leaner  mixtures  than  would  ordinarily  be 
used  must  be  employed  to  prevent  pre-ignition,  with  a  correspond- 
ing loss  in  the  value  of  p{.  Beyond  r  =  6  the  gain  in  Ee  is  small 
and  at  r  =  10  it  practically  ceases  to  increase.  Hence  we  con- 
clude that  for  combustion  at  constant  volume  the  use  of  values  of  r 
greater  than  about  8,  for  which  the  compression  pressure  equals 
about  225  pounds,  is  no  longer  accompanied  by  any  useful  gain  in 
the  economic  efficiency  of  the  machine.  This  statement  does  not 
apply  to  combustion  at  constant  pressure  because  its  Ec  follows 


THEORETICAL   CYCLES  83 

a  different  law,  and  Em  decreases  more  slowly  on  account  of  the 
generally  greater  value  of  p.. 

Finally,  in  laying  out  an  Otto  cycle,  to  obtain  high  engine 
capacity  per  unit  volume  of  cylinder  means  making  the  maxi- 
mum pressure  as  high  as  possible  to  obtain  a  high  value  of  p.. 
With  fuel  mixtures  which  cannot  stand  a  high  amount  of  com- 
pression this  would  mean  the  use  of  rich  gas  mixtures.  Where 

j    ^  •  ^  e  max.  pressure 

the  compression  can  be  made  higher,  the  ratio  of  -  — , 

comp.  pressure 

instead  of  being  from  4-5,  may  be  profitably  made  from  2.5  to  3 
by  the  use  of  leaner  mixtures,  so  that  the  maximum  pressure 
shall  be  in  the  neighborhood  of  say  450  pounds.  The  chances 
are,  as  the  gas  engine  develops,  that  higher  maximum  pressures 
will  be  employed,  but  according  to  Giildner  the  use  of  working 
pressures  exceeding  600  pounds  is  neither  economical  nor  safe. 


CHAPTER  IV 

THE  VARIOUS  EVENTS  OF  THE  CONSTANT  VOLUME  AND  THE 
CONSTANT-PRESSURE  CYCLES  AS  MODIFIED  BY  PRACTICAL 
CONDITIONS 

1.  IN  the  previous  chapter  the  various  cycles  were  discussed 
and  compared  on  theoretical  grounds.     For  this  purpose  several 
things  were  assumed  which  in   practice   are   only  approximately 
true;  thus  compression  and  expansion   lines  were  assumed  adi- 
abatic  and  the  surrounding  walls  impermeable  to  heat.    It  is,  how- 
ever, true  that  the  heat  interchange  between  the  charge  and  the 
walls  may  be  such  as  to  give  a  line  on  a  diagram  which  strictly 
follows  the  adiabatic  law.    Such  a  line  is  by  some  writers  called  a 
false  or  pseudo-adiabatic.    Again  it  has  been  assumed  in  the  theo- 
retical discussion  that  ignition  is  perfect,  that  the  composition  of 
the  charge  is  uniform,  and  that  combustion  is  complete  and  per- 
fect ;  none  of  these  things  quite  obtain  in  practice  and  all  the  va- 
riations have  their  influence  upon  engine  performance.    Thus  it 
happens  that  the  cyclic  efficiency  above  computed  is  in  any  given 
case  never  realized,  but    that  the  actual  thermal  efficiency  is  al- 
ways less  than  Ec. 

The  following  paragraphs  will  point  dut  these  modifications 
more  in  detail. 

2.  The  four-stroke  Otto  cycle. 

(a)  THE  SUCTION  STROKE.  At  the  end  of  the  exhaust  stroke, 
the  clearance  volume  V c,  Fig.  4-1,  is  filled  \\ith  burned  gases 
under  a  pressure  pe  and  a  temperature  T ' e.  The  weight  of  these 
gases  can  only  be  approximately  computed,  since  nothing  definite 
is  known  of  the  temperature  T  e.  It  is  in  most  cases  probably 
between  12-1400  degrees  Fahrenheit,  while  the  pressure  pe  in 
well-designed  machines  may  be  from  16-18  pounds  absolute, 
but  circumstances  may  alter  these  figures  considerably.  At 
the  commencement  of  the  suction  stroke  the  pressure  falls 
from  pe  to  the  suction  pressure  ps  along  a  curve  deter- 
mined by  the  re-expansion  of  the  burned  gases  in  the 
clearance  spaces.  Only  after  this  re-expansion  will  the  fresh 
charge  be  drawn  into  the  cylinder.  It  is  thus  seen  that  the 

84 


THEORETICAL   CYCLES  MODIFIED   BY   PRACTICE     85 

volumetric    efficiency,   Ev,   of  the  cylinder,    that    is,   the   ratio 

volume  of  fresh  mixture  ,     , .  '.  , 

—7 — r—    — j; — \ —         -,->  depends  directly  upon  the  weight 
volume  of  piston  displacement 

of  burned  gases  remaining,  thus  affecting  cylinder  capacity.  If 
through  bad  form  of  combustion  chamber,  too  small  an  exhaust 
opening,  or  a  restricted  exhaust  pipe,  the  exhaust  pressure  should 
be  kept  too  high,  or  too  much  burned  gas  remain  behind,  this  effect 
of  re-expansion  will  be  more  marked  than  above  stated.  A  too 
early  closure  of  the  exhaust  valve  may  have  the  effect  shown  in 
Fig.  4-1  in  dotted  line.  It  is  evident,  however,  that  in  the  ordinary 
four-cycle  engine  without  scavenging  this  loss  of  volumetric  effi- 
ciency will  always  be  present,  depend  ing  upon  the  clearance  volume. 


FIG.  4-1. 

A  second  factor  affecting  the  volumetric  efficiency  of  the 
cylinder  is  the  suction  pressure  ps.  At  the  end  of  the  suction 
stroke  the  cylinder  contains  a  volume  of  gas,  vt,  made  up  partly 
of  burned  gas  and  partly  of  fresh  mixture,  under  a  pressure  ps. 
The  compression  stroke  raises  this  amount  of  gas  to  the  pressure 
pc  with  a  volume  vc.  The  compression  curve  crosses  the  atmos- 
pheric line  when  the  stroke  volume  is  only  vs,  and  not  the 


full  volume  vr.     Hence  the   volume  v 


represents  a  loss  in 


volumetric  efficiency,  and  this  loss  is  the  greater  the  smaller  ps. 
It  follows  that  the  inlet  pipes  and  valves  should  be  so  designed  as  to 
cause  a  minimum  suction  Bunder-pressure,"  that  is,  to  keep  ps  as 
close  to  atmospheric  pressure  as  possible.  This  also  makes  clear 
why  vaporizers  and  carbureters  always  decrease  engine  capacity 
somewhat. 


86  INTERNAL  COMBUSTION  ENGINES 

Thus  there  is  a  loss  of  volumetric  efficiency,  and  hence  of 
engine  capacity,  at  each  end  of  the  suction  line.  The  real  volu- 
metric efficiency,  Ev,  is  found  in  any  given  case  by  dividing  the 
volume  represented  by  the  line  a-b,  measured  along  the  atmos- 
pheric line,  by  the  volume  vs  of  the  piston  displacement. 

Attention  should  at  this  point  be  called  to  the  fact  that  cer- 
tain systems  of  speed  regulations  depend  upon  the  variation  in 
the  suction  pressure.  By  throttling  the  mixture  from  the  begin- 
ning of  the  stroke,  or  by  cutting  off  the  supply  completely  at  a 
given  point  in  the  stroke,  ps  is  increased  or  decreased  depending 
on  the  load  on  the  engine,  thus  directly  controlling  the  charge 
volume,  and  hence  the  engine  capacity.  This  is  explained  more 
in  detail  in  the  chapter  on  governing. 

Since  it  is  quite  evident  that  neither  the  loss  by  re-expansion 
or  that  due  to  the  suction  pressure  at  the  end  of  the  suction  stroke 
can  be  entirely  avoided,  it  becomes  interesting,  at  least  from  the 
point  of  design,  to  know  approximately  \vhat  values  of  Ev  to 
expect  in  different  types  of  engines.  Naturally  Ev  decreases 
as  engine  speed  increases,  because  since  high-speed  engines 
are  usually  small  engines,  the  difficulty  of  placing  valve  openings 
large  enough  to  prevent  serious  throttling  of  the  charge  becomes 
greater  as  speeds  increase.  Computations  are  of  little  avail  in 
this  matter  since  little  is  definitely  known  of  the  temperature 
of  the  charge  at  the  end  of  the  suction  stroke.  For  that  reason 
more  reliance  is  to  be  placed  in  figures  based  upon  practical 
experience.  The  following  table  is  due  to  Giildner: 

Ev  ps 

Ibs.  persq.  inch 

absolute 

1.  blow-speed  engines  with    mechanically  oper- 

ated inlet  valve 88  -  .93         12.9  -  13.7 

2.  Slow-speed  engines  with  automatic  inlet  valve     .80  -  .87         12.5  -  13.2 

3.  High-speed    engines  with  mechanically  oper- 

ated inlet  valve 78  -  .85         11.7  -  12.5 

4.  High-speed  engines  with  automatic  inlet  valve     .65  —  .75         11.4  —  12.2 

5.  Very  high-speed  engines  with  automatic  inlet 

valves  and  air  cooling 50  -  .65  8.8-11.0 

Suction  gas  generators  and  vaporizers  may  in  unfavorable 
cases  decrease  the  above  figures  for  Ev  as  much  as  .05. 

(6)  THE  COMPRESSION  STROKE.  —  The  compression  line  may 


THEORETICAL  CYCLES  MODIFIED  BY  PRACTICE     87 

be  taken  to  follow  the  general  law  pvn  =  constant.  During  the 
first  part  of  the  stroke  there  is  probably  a  flow  of  heat  from  the 
walls  to  the  comparatively  cool  charge,  but  this  is  soon  over- 
balanced by  the  heat  of  compression,  so  that  during  the  last  and 
greatest  part  of  the  stroke  the  flow  is  into  the  walls.  The  com- 

y 
pression  curve  is  therefore  rarely  an  adiabatic  pv    =  constant, 

C1 
where  y  =  ~  ,  as  computed  for  the  charge.     In  most  cases  the 

L>v 

line  is  intermediate  between  an  adiabatic  and  an  isothermal,  and 
strictly  also  the  value  of  the  exponent,  n,  is  not  constant  along  the 
entire  line.  The  value  of  n  in  actual  cases  lies  between  1.30  and 
1.38,  with  an  average  of  about  1.35.  In  cases  of  very  ineffective 

C1 

cooling  n  may  exceed  y  =  -~  .     It  should  also  be  noted  that 

Cw 

leaky  pistons  and  valves  cause  a  flattening  of  the  compression 
curve,  which  apparently  decreases  the  true  value  of  n. 

From  the  equation  pvn  •-=  constant,  we  may  derive  the  follow- 
ing equation  for  the  absolute  pressure  pc  at  the  end  of  compres- 
sion, see  Fig.  1. 


The  absolute  temperature  at  the  pressure  pc  will  be 


y   =  T  I  £l 


n          m      n-. 


n 


This  equation  requires  an  assumption  for  the  value  of  T  s,  the 
temperature  at  the  end  of  the  suction  stroke.  As  already  stated, 
not  a  great  deal  is  known  about  this.  S.  A.  Moss  states  that 
experiments  have  shown  it  to  be  between  200-300  degrees 
Fahrenheit,  that  is,  660-760  degrees  absolute,  but  gives  no  details. 
Schottler  in  his  examples  on  type-cycles  assumes  in  most  cases 
350  degrees  Centigrade  absolute,  =  632  degrees  Fahrenheit  absolute. 

The  clearance  volume  required  to  produce  a  pressure  pc  and  a 
temperature  Tc  will  be 


The  following  table  shows  values  for  the  absolute  compression 
pressure,  pc  and  the  end  temperature  Tc  for  various  values  of  n, 
of  r,  the  ratio  of  compression,  and  of  T  s.  The  value  of  ps  has  been 
assumed  at  12.5  pounds  absolute: 


88 


INTERNAL  COMBUSTION  ENGINES 


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THEORETICAL   CYCLES  MODIFIED   BY   PRACTICE     89 

It  has  already  been  shown  in  the  previous  chapter  how  the 
cyclic  efficiency  and  consequently  also  the  thermal  efficiency  of 
an  engine  depends  upon  the  compression  pressure.  It  has  also 
been  shown  that  there  are  commercial  limits  to  the  compression 
pressure  due  to  pre-ignition  of  charge.  As  regards  pre-ignition 
of  charge,  which  is  to  be  distinguished  from  back  firing  or  explo- 
sions in  the  exhaust  pipe,  the  greater  danger  of  this  exists  with 
fuel  mixtures  high  in  hydrogen.  Hydrogen,  next  to  acetylene, 
possesses  the  lowest  ignition  point  of  any  of  the  gaseous  fuels 
commonly  employed.  Hence  illuminating  gas  with  about  45 
per  cent  by  volume  of  hydrogen  is  much  more  liable  to  pre-ex- 
plosion  under  the  temperature  of  compression  than  a  producer 
gas  with  15  per  cent.  Hence  we  may  use  a  higher  compression 
pressure  in  the  case  of  the  latter  gas,  and  may  expect,  and  actually 
obtain,  a  higher  thermal  efficiency  in  practice.  With  gases  very 
rich  in  CO  and  low  in  hydrogen  there  is  little  danger  of  pre-igni- 
tion even  up  to  the  commercial  limit  of  high  pressures.  Lucke 
estimates  that  for  every  5  per  cent  of  hydrogen  that  the  gas  con- 
tains 15  pounds  should  be  subtracted  from  the  otherwise  allow- 
able compression  pressure.  In  general  it  should  be  borne  in 
mind,  and  this  applies  to  all  fuel  mixtures,  the  better  and  more 
effective  the  cooling  of  the  cylinder,  the  higher  can  be  the  com- 
pression without  danger  of  pre-ignition.  Anything  which  draws 
down  the  temperature  during  compression,  as  water  injection, 
is  also  favorable  to  the  same  thing.  A  case  in  point  is  Banki's 
method  of  water  injection  with  gasoline  as  fuel,  b}'  which  means 
compression  pressures  could  be  employed  which  gave  thermal 
efficiency  results  equal  to  the  best  obtained  on  lean  gases. 

Premature  explosions  are  sometimes  directly  due  to  faulty 
design  of  the  combustion  chamber.  Any  projecting  point  or 
edge  in  the  chamber  which  cannot  be  effectively  water-cooled 
may  become  red  hot  under  compression,  and  thus  locally  raise 
the  temperature  high  enough  to  cause  pre-ignition.  This  action 
is  so  certain  that  it  has  been  proposed  to  use  it  as  a  method  of 
ignition  by  placing  a  projection  on  the  piston  face.  It  was  found 
that  while  this  scheme  would  work,  it  was  not  susceptible  of  con- 
trol, and  was  abandoned. 

The  following  table  shows  the  safe  compression  pressures  in 
use  with  the  fuels  commonly  employed,  as  given  by  Lucke,  The 


90 


INTERNAL  COMBUSTION  ENGINES 


second  column  gives  the  percentage  of  clearance  required  to 
produce  the  pressure  pc  in  terms  of  the  piston  displacement. 
This  column  has  been  computed  assuming  ps  =  13  Ibs.  absolute 
and  n  =  1.35. 


Fuel 

Compression 
Pressure 
Lbs.  by  gage 

%  Clearance  in 
terms  of  Piston 
Displacement 

Gasoline: 
Auto-engines  with  carbureters,  cooling  not 
very  effective  high  speeds.    . 

45  -  95 
Ave    65 

35 

Gasoline  : 
Stationary,  slow-speed  engines,  more  effec- 
tive cooling  but  usually  less  simple  com- 
bustion chamber  

60  -  85 
Ave      70 

32 

Kerosene  : 
Hot  bulb  injection  and  ignition        .  .  . 

30  —  75 

35  —  40 

Kerosene: 
Previously  vaporized  in  devices  not  requir- 
ing a  vacuum       .  . 

45  -  85 
Ave      65 

35 

Natural  Gas    
Natural  Gas  : 
Average  for  large  and  medium  engines.  .  . 
Illuminating  gas         .        

75  -  130 

Ave.,  115 
60  —  100 

22 

Producer  Gas       . 

Ave.,    80 
100  -  160 

26 

Producer  Gas: 
In  large  engines  water-cooled  on  pistons 
and  valves  

Ave.,  135 

20 

Blast  Furnace  Gas 

120  -  190 

Ave.,  155 

17 

(c)  THE  COMBUSTION  LINE.  —  The  shape  of  the  combustion 
line  depends  primarily  upon  the  interrelation  of  three  things: 
composition  of  charge,  point  of  ignition,  and  piston  speed. 

For  every  fuel  there  is  a  certain  fuel-air  mixture  which  gives 
the  greatest  rate  of  flame  propagation,  i.e.,  the  most  rapid  com- 
bustion. Any  further  admixture  of  neutral  gases,  whether  these 
be  air  or  burned  gases,  results  in  a  slower  combustion,  until  there 
comes  a  time  when  ignition  fails.  Suppose,  therefore,  that  in  any 
given  engine  with  full  throttle,  constant  speed,  and  proper  igni- 


THEORETICAL   CYCLES  MODIFIED  BY   PRACTICE     91 


tion,  we  obtain  diagram,  Fig.  4-2,  a.    Now  if  the  throttle  is  partly 

closed,  making  the  dilution  of  the  charge  by  the  burned  gases 

greater  than  before,   card,  Fig.  4-2,  6, 

results.    Further  closure  of  the  throttle 

makes    the    combustion    still    slower, 

Fig.  4-2,  c.     Similar  effects  would  have 

been  obtained  with  full  throttle  if  the 

proportion  of  air  in  the  fresh  charge  be 

seriously  increased. 

For  proper  combustion  the  time  of 
ignition  should  be  so  chosen  that  the 
combustion  line  is  vertical  or  nearly 
so.  This  means  that  every  different  fuel 
mixture  and  every  different  piston  speed 
will  have  its  own  proper  point  of 
ignition.  For  that  reason  the  ignition 
apparatus  in  every  engine  should  be 
made  adjustable,  because  the  only  way 
to  determine  the  proper  time  is  by  trial. 
For  small  gasoline  engines  this  adjusting 
may  be  done  by  ear,  since  the  proper 
point  of  ignition  corresponds  nearly 
with  the  highest  speed,  for  a  given 
throttle  position.  For  more  accurate 
work  the  indicator,  preferably  with  a 
constant-speed  drum  motion,  should  be 
used.  It  will  in  general  be  found  when 
ignition  is  right  that  it  occurs  some 
time  before  the  piston  has  reached  the 
dead  center,  the  amount  of  this  lead  de- 
pending upon  the  mixture  and  the 
piston  speed  as  above  stated.  What  im- 
properly timed  ignition  results  in  is 
shown  in  a  diagram,  Fig.  4-3,  given  by 
Clerk.  With  proper  ignition  the  normal 
diagram  is  indicated  by  a.  As  the  time 
of  ignition  is  made  later  and  later, 
cards  6,  c  and  d  result,  in  the  last 
case  flame  propagation  starting  so  FIG.  4-2. 


92 


INTERNAL  COMBUSTION   ENGINES 


late  that  it  barely  overtakes  the  piston  before  the  end  of  the 
stroke. 

If  instead  of  changing  the  time  of  ignition  the  piston  speed 
had  been  increased,  effects  very  similar  to  those  of  Fig.  4-3 
would  have  been  obtained. 

Thus  the  dependence  of  the  shape  of  the  combustion  line  upon 
the  three  factors  mentioned  at  the  outset  is  clear. 

The  maximum  pressure  attained  during  combustion  depends 
upon  the  heating  value  of  the  charge.  With  all  conditions  favor- 
able, the  maximum  pressure  should  be  reached  at  or  before  one- 
tenth  stroke.  The  rich  fuel  mixtures,  those  for  illuminating 
gas,  natural  gas,  gasoline,  etc.,  show  rapid  combustion.  They 


FIG.  4-3. 

cannot  in   general   stand    high    compression,   and    the  ratio    of 

maximum   pressure  ,  ... 

— ,  simply  called  the  pressure  ratio,  is  usually 
compression   pressure 

high,  between  3  and  5.  The  naturally  leaner  fuels  like  producer 
gas  and  blast  furnace  gas  ignite  better  when  highly  compressed, 
but  on  account  of  the  generally  low  heating  value  of  their  fuel 
mixtures  the  pressure  ratio  for  these  gases  is  usually  less,  between 
1.5  and  3. 

The  maximum  explosion  pressure  px,  Fig.  4-1,  even  assuming 
complete  combustion  at  constant  volume,  is  in  no  actual  case  as 
high  as  that  computed  on  theoretical  grounds  for  the  heat  received 
by  the  cycle.  There  may  be  several  reasons  for  this.  One  is  un- 
doubtedly the  loss  of  heat  to  the  jacket  water  during  explosion. 
This  amount  of  heat  is  a  dead  loss  since  it  does  not  even  enter 
the  cycle.  It  is  something,  however,  which  cannot  be  avoided, 
since  cooling  is  a  necessity  for  other  reasons.  Another  is  due  to 
the  undoubted  fact  that  the  specific  heat  of  the  gases  increases 


THEORETICAL   CYCLES  MODIFIED  BY  PRACTICE     93 

with  the  temperature.  We  can  not,  however,  as  yet  mathemati- 
cally gage  this  effect,  because  nothing  definite  is  known  of  the 
law  of  increase.* 

Another  theory  to  account  for  the  failure  to  realize  theoreti- 
cally maximum  pressure  assumes  that  combustion  is  not  com- 
plete, that  is,  that  not  all  of  the  heat  of  the  charge  is  liberated 
when  the  piston  starts  forward.  This  results  in  after-burning, 
which  will  be  considered  later.  It  is  quite  likely  that  in  most 
cases  these  three  things  combine  to  keep  the  observed  pressure 
below  that  calculated. 

Assume  that  the  combustion  takes  place  at  constant  volume, 
and  let  px  and  Vc,  Fig.  4-1,  be  the  pressure  and  volume  at  the 
end  of  the  explosion. 


mi  x       ,  m 

Then  px  =  ^—  and  Tx  = 


PC 


If  the  combustion  line  is  other  than  vertical,  as  indicated  by 
dotted  line  in  Fig.  4-1,  let  px  ,  Tx'  and  Vx'  be  the  data  for  the 
end  of  the  combustion.  The  above  equations  then  become 


If  in  the  above  equations  the  values  of  px  or  px,  are  taken 
from  actual  diagrams,  the  equations  for  Tx  or  Txl  will  give  real 
temperatures.  But  if  px  should  be  computed  from  one  of  the 
theoretical  diagrams  of  the  previous  chapter,  then  the  value  of  Tx 
should  be  multiplied  by  a  factor  which  expresses  how  much  the 
real  value  of  px  falls  below  the  theoretical  value  of  px  due  to 
imperfections  of  combustion.  This  factor  is  approximately  equal 
to  the  ratio 

Indicated  thermal  efficiency 
cyclic  efficiency 

An  idea  of  the  maximum  pressures  px  or  p/  existing  in  the 
cycle  may  be  gained  by  considering  that  in  most  cases  the  ratio 

—  can  be  made  equal  to  3.     Turning  to  the  table,  page  88,  we 

PC 

*  See  Chapter  X. 


94  INTERNAL  COMBUSTION   ENGINES 

see  that  for  n  =  1.35,  and  r  =  6,  pc  is  equal  to  about  140  Ib. 
absolute.  Thus  px  would  be  about  3  X  140  =  420  Ib.  The 
temperature  T 'x,  assuming  Ts  =  700  degrees,  which  for  the  same 
values  of  n  and  r,  makes  T  =1114,  would  then  be  about 

Tx  =  42°**114  =  3342°  F.  absolute. 

J.4U 

The  following  figures  give  a  few  of  the  characteristic  diagrams 
for  various  fuels. 


FIG.  4-4. 

FIG.  4-4.  From  Struthers-Wells  hit-and-miss  engine.  ll|"x  18",  30  H.P., 
200  r.p.m.,  natural  gas.  Card  good  throughout,  compression  80  Ib.,  max. 
pressure,  320  Ib.  Pressure  ratio  W  =  3.5. 


FIG.  4-5. 

FIG.  4-5.  From  Struthers-Wells  automatic  engine,  16$"  x  22",  150  H.P., 
200  r.p.m.,  natural  gas,  full  load.  Card  good,  compression  96  Ib.,  max., 
pressure  330  Ib.  Pressure  ratio  ftf  =  3.1. 


THEORETICAL   CYCLES  MODIFIED  BY   PRACTICE     95 


FIG.  4-6.  From  Stock- 
port  engine.  Given 
by  Clerk,  the  Gas  and 
Oil  Engine,  p.  321. 
9f"  x  17",  9  h.p.,  182 
r.p.m.  Illuminat- 
ing gas.  Compression 
90  lb.,  max.  pressure 
270  lb.  Pressure  ratio 
=  2.7. 


FIG.  4-6. 


FIG.  4-7.  FromHornsby- 
Akroyd  kerosene  en- 
gine. 6  H.P.,  225 
r.p.m.,  Card  at  about 
J  load.  Hot  bulb 
vaporization,  hence 
pressures  low.  Com- 
pression 45  Ibs.,  maxi- 
mum pressure  116  lb. 
Pressure  ratio  =  VV 
=  2.2. 


FIG.  4-7. 


FIG.  4-8.  Card 
from  a  gasoline 
engine  given  by 
Lucke,  Gas  En- 
gine Design,  p.  71. 
Vapor  prepared 
outside  cylin- 
der. Compression 
80  lb.,  maximum 
pressure  372  lb. 
Pressure  ratio  V/ 
=  4.07. 


FIG.  4-8. 


96 


INTERNAL  COMBUSTION   ENGINES 


FIG.  4-9. 

FIG.  4-9.     Taken  from  Koerting  engine.     700    H.P.     Blast    furnace    gas. 
Max.  pressure  242   lb.,   compression  pressure  127   lb.,  Pressure  ratio  = 

m  =  1.8. 


FIG.  4-10. 

FIG.  4-10.  From  American  Crossley  producer  gas  engine,  given  by  Langton. 
18J  x  24",  65  K.W..  200  r.p.m.  Hit-and-miss  governor.  Gas  rather  high 
in  H  and  low  in  CO,  hence  compression  low.  Compression  83  lb.,  maximum 
pressure  248  lb.  Pressure  ratio  W  =  2.7. 

The  following  two  diagrams  show  abnormal  conditions: 


FIG.  4-11. 

FIG.  4-11.  Pronounced  case  of  pre-ignition  in  6  H.P.  Hornsby-Akroyd 
kerosene  engine  due  to  too  high  compression.  This  was  cured  by  the 
addition  of  a  little  water  to  the  charge. 


THEORETICAL   CYCLES  MODIFIED   BY   PRACTICE     97 


FIG.  4-12. 

FIG.  4-12.  Case  of  back-firing  as  distinguished  from  pre-ignition.  Power, 
Oct.  15,  1900.  Explosion  in  the  suction  pipe  at  a  during  the  suction  stroke. 
Observed  in  an  engine  which  attempted  scavenging  by  means  of  os- 
cillations of  burned  gases  in  the  exhaust  pipe.  Back-firing  more  often 
occurs  in  the  exhaust  pipe  due  to  accumulation  of  unburned  gas. 

(d)  THE  EXPANSION  LINE.  —  The  expansion  line,  like  the 
compression  line,  may  be  taken  to  follow  a  general  law  p  vn  = 

C 
constant,  in  which  n  is  rarely  equal  to    y=     *,  for  the  burned 

CMP 

gases.     Assuming  that  combustion  is  complete  when  the  piston 

starts  forward,  the  loss  of  heat  to  the  jacket  during  expansion 
should  cause  the  expansion  line  to  lie  below  the  adiabatic,  that  is, 
n  should  be  greater  than  y.  (It  should  be  remembered  in  this 
connection  that  leaky  pistons  and  valves  cause  an  increase  in  the 
true  value  of  n.)  Now  it  is  very  often  found  that  the  expansion 
line  falls  off  much  more  slowly  than  this,  coinciding  now  and  then 
with  the  adiabatic,  but  very  often  lying  between  this  and  the 
isothermal,  that  is,  n  is  less  than  y.  The  explanation  of  this 
phenomenon  has  been  held  to  be  an  evolution  of  heat  along  the. 
expansion  line  equal  to  or  exceeding  the  loss  of  heat  to  the  jacket 
during  this  period.  Several  theories  have  been  advanced  to 
explain  this. 

The  older  machines  of  Lenoir  and  Hugon  showed  values  of 
the  exponent  n  for  the  expansion  line  between  1.4  and  1.6,  while 
the  earlier  Otto  machines  showed  values  approximating  1.3.  To 
explain  this,  Otto,  and  after  him,  Slaby,  at  least  for  a  time, 
advanced  the  theory  of  stratification.  It  was  supposed  that  the 
charge  of  a  4-cycle  machine  could  be  so  arranged  as  to  have 
practically  nothing  but  burned  gases  against  the  piston,  next 
practically  air,  then  a  layer  of  poor  mixture,  and  finally  near  the 
igniter  the  fuel  mixture  in  its  full  strength.  It  was  further 


98  INTERNAL  COMBUSTION  ENGINES 

assumed  that  this  arrangement  was  disturbed  but  little  during 
compression.  Hence  ignition  was  sure;  but  as  the  combustion 
progressed  and  reached  the  leaner  layers  of  mixture,  it  became 
more  and  more  slow,  was  not  completed  when  the  piston  started 
forward,  and  was  continued  along  the  expansion  line,  showing  a 
so-called  after-burning.  Thus  Otto  attempted  to  explain  the 
somewhat  slower  rise  of  the  combustion  line  and  the  absence  of 
the  serious  shock  at  the  moment  of  explosion  in  his  gas  engines. 
In  the  fight  against  the  Otto  patent,  tests  were  made  by  the 
Deutz  Company,  by  Dewar  and  by  Teichman,  all  of  which  seem 
to  support  Otto's  claim  of  stratification.  Slaby  defended  it 
vigorously.  It  has,  however,  been  pretty  clearly  shown  to-day 
that,  while  stratification  is  not  at  all  impossible,  in  fact  it  is  not 
easy  to  get  a  uniform  mixture,  it  cannot  have  any  marked  effect 
upon  economy  or  performance;  that  is,  the  diagrams  would  not 
be  very  far  different.  The  opinion  of  the  best  writers  of  to-day 
leans  toward  the  requirements  of  most  uniform  mixture  and  rapid 
combustion.  Clerk  has  attempted  to  show  that  some  heat  is 
" suppressed"  during  the  combustion  period  in  every  gas  engine 
and  released  along  the  expansion  line,  although  to  attempt  to 
express  these  quantities  in  thermal  units  would  seem  superfluous 
in  view  of  the  fact  that  we  know  nothing  definite  of  the  variation 
of  specific  heat  at  high  temperatures.  It  would  seem,  therefore, 
that  after-burning,  if  it  exists,  is  not  a  peculiarity  common  to 
Otto  engines  only.  It  is  merely  evidenced  more  strongly  in  the 
Otto  diagrams  by  the  fact  of  higher  piston  speeds  and  porportion- 
ately  smaller  enveloping  surface,  giving  less  time  and  opportunity 
for  heat  losses  along  the  expansion  line,  as  compared  with  gas 
engines  before  Otto's  time.  Hence,  as  Clerk  puts  it,  the  slow 
dropping  of  the  expansion  line  is  not  the  cause  of  the  greater 
economy  of  the  Otto  engine,  but  rather  the  effect  and  evidence  of  it. 
The  second  explanation  of  the  supposed  after-burning  rests  on 
the  so-called  dissociation  theory.  It  has  been  shown  by  Bunsen 
that  a  composite  gas  breaks  up  into  its  elements  when  the  tem- 
perature exceeds  certain  limits.  Conversely,  chemical  combina- 
tions, such  as  combustion,  can  no  longer  take  place  when  this 
temperature  limit  is  reached.  This  theory  applied  to  the  gas 
engine  would  mean  that  at  the  inner  piston  position,  if  the  tem- 
perature rises  to  the  limit,  combustion  no  longer  takes  place, 


THEORETICAL   CYCLES  MODIFIED  BY  PRACTICE     99 

but  just  as  soon  as  the  piston  starts  forward,  resulting  in  a  drop 
of  both  temperature  and  pressure,  combustion  again  ensues  and 
is,  by  the  same  method,  continued  along  the  expansion  line  until 
no  combustible  remains.  Clerk  strongly  leans  to  this  view  of  the 
matter.  But  it  has  been  pretty  definitely  shown  that  the  tem- 
peratures in  gas  engines  rarely  exceed  28-3000  degrees  Fahrenheit, 
and  that  these  temperatures  are  below  the  dissociation  limit.  It  has 
also  been  pointed  out  by  Schottler  that  if  this  theory  holds  good  the 
expansion  line  should  be  an  isothermal  as  long  as  there  is  com- 
bustion. It  may  therefore  be  concluded  that  dissociation  plays  but 
a  small  part  in  the  combustion  phenomena  found  in  gas  engines. 

Witz,  in  some  tests  made  with  an  engine  whose  piston  speeds 
could  be  varied,  found  that  in  each  case  after-burning  occurred, 
but  that  the  combustion  was  the  more  rapid  and  the  maximum 
pressure  the  higher  (that  is,  after-burning  the  less  noticeable), 
the  greater  the  piston  speed  and  the  warmer  the  jacket  walls. 
Thus  he  concludes  that  after-burning  largely  depends  upon  the 
influence  of  the  walls.  Slaby,  corroborated  by  E.  Meyer,  on  the 
basis  of  other  tests,  has  tried  to  show  that  these  conclusions  of 
Witz  are  not  generally  applicable,  but  on  weighing  the  evidence, 
and  in  the  light  of  later  achievements,  it  must  be  concluded  that 
they  and  the  principle  based  upon  them,  i.e.,  rapid  combustion 
of  the  leanest  possible  mixture  at  the  greatest  possible  piston 
speed,  at  least  represent  a  step  in  the  right  direction  for  gas 
engine  economy. 

From  the  above  it  is  quite  evident  that  none  of  the  theories 
advanced  explain  satisfactorily  all  of  the  phases  of  the  question 
of  after-burning,  the  occurrence  of  which  must  be  held  as  proven, 
especially  in  the  light  of  later  tests.  Schottler,  indeed,  has 
offered  another  explanation  for  the  so-called  abnormal  position 
of  the  expansion  line  by  showing  that  a  natural  solution  of  the 
question  may  be  found  in  the  variation  of  the  specific  heat  of  the 
expanding  gases  with  temperature.  Some  figures  quoted  by  him 
show  that  this  may  be  the  case,  but  before  the  idea  of  after-burn- 
ing can  be  dispensed  with,  a  great  deal  more  experimental  work 
is  needed  and  desirable. 

The  requirements  for  best  efficiency  of  combustion  and  ex- 
pansion have  already  been  briefly  explained.  In  a  little  greater 
detail  they  are  as  follows: 


100  INTERNAL   COMBUSTION  ENGINES 

1.  Highest  possible  compression  pressure  before  ignition.     The 
effect  of  this  is,  (a)  less  admixture  of  burned  gases  to  the  fresh 
charge,  (b)  less  loss  to  jacket  because  smaller  volume  is  involved,  (c) 
greater  mean  effective  pressure,  (d)  greater  ease  of  ignition  of  charge. 

2.  Pure  and  uniform  mixture  and  rapid  combustion  to  avoid 
after-burning.     The  bad  effect  of  after-burning  is  due  to  the  great 
jacket  loss  along  the  expansion  line,  and  its  effect  has  been  com- 
pared by  Koerting  to  that  of  a  leaky  valve  in  a  steam  engine. 

3.  Avoid  external  cooling.     This  of  course  cannot  be  entirely 
eliminated.     But  since  the  amount  of  heat  lost  by  cooling  is  a 
function  of  both  time  and  superficial  surface,  this  requirement 
calls  for  high  piston  speeds  and  a  form  of  cylinder  in  which  the 

superficial  surface  . 

ratio  -  -  is  the  smallest  possible, 

volume 

To  return  to  the  expansion  line,  at  the  moment  the  exhaust 
valve  opens,  the  gases  have  expanded  to  a  volume  Vy,  with  a 
pressure  py,  and  a  temperature  TyJ  see  Fig.  4-1.  We  may  write 


The  ratio  —  is  the  real  ratio  of  expansion.'    The  expressions  for 

^c 

the  value  of  py  and  Ty  for  the  constant-pressure  cycle  are  anal- 
ogous; care  should  be  taken,  however,  to  use  the  proper  ratio  of 
expansion,  which  in  this  case  is  quite  different  from  the  ratio  of 
compression.  In  the  case  of  the  Otto  cycle  the  ratio  of  ex- 
pansion is  in  most  instances  nearly  as  great  as  the  ratio  of 
compression  r,  arid  we  may  therefore  write,  from  the  above  ex- 
pression for  p 

py  -  Px 

rn 

It  appears  from  this  equation  that,  with  px  remaining  the 
same,  the  terminal  pressure  decreases  as  the  compression  in- 
creases. In  practice,  however,  the  terminal  pressure  in  most 
cases  shows  an  increase  as  compression  is  increased,  due,  no 
doubt,  to  the  fact  that  px  also  increases  with  compression,  unless 
the  mixture  is  made  correspondingly  leaner. 

(e)  THE  EXHAUST  STROKE.  —  The  velocity  of  efflux  of  gas 
at  the  instant  the  exhaust  valve  opens  is  very  high,  approximat- 
ing 25-3500  ft.  per  second.  The  valve  should  start  to  open  at  about 


THEORETICAL   CYCLES  MODIFIED 


T9<r  out  stroke,  and  the  opening  should  be  of  such  size  that  equaliza- 
tion of  pressure  is  practically  established  by  the  time  the  outer 
dead  center  is  reached.  Too  small  an  opening  means  increased 
lost  work  due  to  higher  back  pressure,  higher  mean  cylinder 
temperatures,  and  less  cylinder  capacity.  To  get  some  idea  of 
the  charging  and  discharging  operations  of  the  four-cycle  cylinder 
it  is  best  to  take  the  so-called  loop  card  with  a  wreak  spring,  say 


FIG.  4-13. 

10-30  Ib.  scale,  with  stop  attached.  Besides  giving  a  measure 
of  the  charging  work,  the  so-called  fluid  friction,  this  also  often 
reveals  defects  in  the  valve  mechanism  and  sometimes  curious 
variations  in  the  exhaust  line,  which,  however,  are  nearly  always 
due,  not  to  the  engine,  but  to  the  exhaust  piping.  The  ideal 
exhaust  line  should  drop  quickly  nearly  to  atmosphere  and  re- 
main so  throughout  the  stroke.  Fig.  4-13,  from  a  16J  X  22 


FIG.  4-14. 

Strut  hers- Wells  automatic  engine  on  natural  gas  at  full  load, 
shows  a  nearly  ideal  exhaust  line  and  in  fact  a  very  good  loop 
card.  Many  loop  diagrams,  however,  show  a  vacuum  at  the 
beginning  of  the  exhaust  stroke.  This  is  undoubtedly  due  to  the 
inertia  of  the  initial  gas  column  once  set  in  motion.  In  some 
cases  the  indication  of  a  vacuum  is  only  very  slight,  in  others  it 
may  last  for  half  the  stroke.  In  fact  some  builders  have  tried  to 


:'i62:  '"INTERNAL  COMBUSTION  ENGINES 

utilize  the  phenomenon  to  help  scavenge  the  cylinder,  but  nothing 
has  resulted  from  it  because  so  many  accidental  conditions  are 
apt  to  interfere  with  the  regularity  of  its  occurrence.  Fig.  4-14 
from  a  6  horse-power  Hornsby-Akroyd  oil  engine  shows  the 
occurrence  of  the  vacuum  very  plainly.  Owing  to  some  pecu- 
liarities in  the  exhaust  pipe,  it  sometimes  happens  that  the  masses 
of  exhaust  gas  in  the  pipe  are  set  into  vibrations  which  cause  a 
recurring  vacuum  in  the  exhaust  line.  Fig.  4-15,  given  by  Giildner, 
shows  a  diagram  from  an  Otto  engine  in  which  this  occurred. 

The  absolute  size  of  the  loop,  i.e.,  the  fluid  friction,  varies 
with  the  method  of  regulation,  and,  in  a  hit-and-miss  engine,  with 
the  load  on  the  engine.  The  effect  of  the  method  of  regulation 
will  be  discussed  in  a  later  chapter.  In  a  hit-and-miss  engine  at 
low  loads  the  cylinder  is  cooler  than  at  high  loads,  and  the  weight 
of  gases  displaced  is  greater,  hence  we  may  expect  a  greater  area 
of  loop  than  at  normal  loads.  Humphrey,  in  a  test  of  a  400 


FIG.  4-15. 

horse-power  Crossley  engine,  determined  a  fluid  friction  loss  of 
15  horse-power  at  full  load,  which  is  ^  =  3.8  per  cent.  When 
the  engine  was  taking  in  air  only,  this  loss  was  33  horse-power, 
but  even  assuming  that  there  was  no  increased  loss  at  say  half 
load,  the  fluid  friction  would  thus  have  been  ^  =  7.5  per  cent. 
It  is  found  in  general  practice  that  fluid  friction  in  hit-and-miss 
engines  represents  from  4-10  per  cent  of  the  engine  power  at  full 
load,  depending  upon  proper  design. 

3.  The  two-stroke  Otto  Cycle.  Fundamentally  there  is  no 
difference  between  the  compression,  combustion  and  expansion 
lines  of  the  four-cycle  and  two-cycle  types  of  engines,  whether 
they  operate  on  the  constant-volume  or  constant-pressure  com- 
bustion principle.  The  difference  between  the  methods  of  opera- 
tion is  principally  that  the  exhaust  and  charging  actions  of  the 
four-cycle  type  are  done  in  another  way  in  the  two-cycle,  and  that 
therefore  the  crank  receives  an  impulse  every  revolution  instead 
of  every  other.  Fig.  4-16  shows  an  idealized  two-cycle  diagram. 


THEORETICAL   CYCLES  MODIFIED  BY  PRACTICE  103 

The  exhaust  opens  as  before  at  a,  the  exhaust  gases  escape,  charg- 
ing commences,  and  is  finished  at  6,  where  compression  commen- 
ces. That  is  the  ordinary  operation.  There  are  some  modifications, 
as  for  instance  fuel  is  pumped  in  under  high  pressure  along  the 
compression  line,  or,  as  in  the  Diesel,  air  alone  is  compressed  and' 
the  fuel  injected  only  when  the  compression  is  completed;  but 
these  are  special  cases.  It  will  be  seen,  therefore,  from  the  dia- 
gram that  in  the  ordinary  case  the  exhaust  and  charging  actions 
must  be  done  during  the  time  that  the  piston  moves  from  a  to  the 
dead  center  position  c,  and  back  again  to  b.  This  time  is  short 
at  best  and  extremely  short  under  high  speeds,  and  therein  lies 
the  whole  difficulty  of  two-cycle  operation. 

The  prime  requirement  of  two-cycle  operation  is  thorough 
scavenging  of  the  cylinder  of  burned  gases,  for  upon  that  depends 


FIG.  4-16. 

not  only  the  volume  of  the  fresh  mixture  that  can  be  taken  in,  but 
also  the  explosibility  of  the  charge.  Too  great  a  remainder  of 
such  gases  not  only  seriously  decreases  the  capacity  of  the  ma- 
chine, but  it  may  even  go  so  far  as  to  prevent  ignition  altogether. 
Thus,  as  Giildner  aptly  says,  the  two-cycle  stands  or  falls  with 
the  perfection  or  imperfection  of  the  scavenging  process.  In  the 
light  of  these  facts  it  is  comparatively  easy  to  point  out  the  re- 
quirement for  good  two-cycle  operation. 

I.  The  exhaust  gases  should  be  at  approximately  atmospheric 
pressure  by  the  time  the  point  c,  Fig.  4-16,  is  reached.  This  reduces 
the  volume  of  the  gases  remaining  in  the  cylinder  and  reduces  the 
work  displacing  them.  For  that  reason  the  exhaust  port  should 
be  of  ample  size,  and  this  explains  why  the  ring  of  ports,  uncovered 
by  the  piston,'  is  so  much  used.  An  exhaust  valve  as  such  is 
done  away  with. 


104  INTERNAL  COMBUSTION  ENGINES 

II.  Scavenging  should  commence  somewhere  between  a  and  c. 
The  scavenging  agents  used  are 

(a)  Air:  (6)  fuel  mixture. 
The  means  by  which  the  scavenging  agent  is  furnished  are 

(a')  Separate  pumps. 

(&')  One  end  of  cylinder  or  cross-head,  used  as  pump. 

(c')  Crank  case  used  as  pump. 

Of  these  combinations,  a-a'  is  undoubtedly  the  best.  It  is 
unquestionable  that  for  thorough  scavenging  some  excess  of  the 
agent  should  be  employed,  and  for  this  only  air  and  not  fuel  mix- 
ture can  be  used.  Now  only  independent  pumps  admit  of  the 
obtaining  of  such  an  excess.  It  is  plain,  however,  that  it  would 
not  pay  to  construct  independent  pumps  for  all  sizes  of  machines, 
hence  they  are  restricted  to  large  or  at  least  medium  powers. 
When  independent  pumps  are  not  employed  there  is  usually 
some  deficiency  of  air.  The  designer,  by  proper  design  of  com- 
bustion chamber  and  valves,  is  then  compelled  to  do  the  best  he 
can  with  the  means  at  hand.  Using  the  front  end  of  the  cylinder  or 
designing  the  cross-head  as  a  pump  is  better  than  using  the  crank 
case  as  such,  mainly  on  account  of  less  leakage,  smaller  clearance 
spaces  and  the  possible  better  arrangement  of  valves.  Fuel  mixtures 
should  under  no  circumstances  be  used  for  scavenging,  except 
where  cheapness  of  machine  is  the  primary  factor.  Hence  the  small 
two-cycle  machine  which  uses  the  fuel  mixture  as  the  scavenging 
agent,  compressing  it  previously  in  the  crank  case.  Such  machines, 
however,  present  no  true  picture  of  two  cycle  operation  or  economy. 

III.  The  scavenging  agent  should  be  of  low  pressure,  and  if 
possible  of  constant  pressure.     Low  pressure  is  required  to  pre- 
vent the  incoming  air  from  piercing  through  and  breaking  up  the 
mass  of  burned  gases.     The  idea  is  to  have  the  scavenging  air 
shove  these  gases  ahead  of  itself  in  a  solid  column.     Constant 
pressure  can  be  maintained  only  by  the  interposition  of  a  reser- 
voir between  the  pumps  and  the  cylinder.     Regarding  the  pres- 
sure of  the  scavenging  air,  however,  a  great  deal  depends  upon 
valve  and  port  construction,  and  speed  of  operation,  hence  nothing 
definite  can  be  said  to  fit  all  cases. 

4.  The  Constant-pressure  cycle.  At  present  this  is  only  carried 
out  as  a  four-stroke  cycle  with  oil  fuel  in  the  Diesel  engine.  Funda- 
mentally the  modification  in  practice  of  the  suction,  compression, 


THEORETICAL   CYCLES  MODIFIED  BY   PRACTICE    105 

expansion,  and  exhaust  lines  do  not  differ  from  those  already  out- 
lined for  the  Otto  cycle.  The  combustion  line  needs  a  little  further 
attention. 

The  first  cycle  proposed  by  Diesel  consisted  of  isothermal  and 
then  adiabatic  compression,  isothermal  combustion  and  adiabatic 
expansion.  This  agrees  with  the  Carnot  cycle.  Difficulties  in 
the  way  of  practical  realization,  however,  lead  to  modifications  of 
this  proposed  cycle  until  the  actual  cycle  of  to-day  has  little  in 
common  with  it.  In  the  first  place,  approximately  adiabatic 
compression,  such  as  is  used  in  any  gas  engine,  was  substituted 
for  the  two  compression  lines  originally  proposed.  The  greatest 
change,  however,  is  in  the  combustion  line.  In  a  lecture  given 
by  Diesel,  a  translation  of  which  was  printed  in  the  Progressive 
Age,  1897,  he  lays  down  as  the  third  requirement  of  his  modified 
cycle  "that  the  fuel  must  be  introduced  gradually  into  the  air, 
which  is  compressed  adiabatically  to  the  combustion  tempera- 
ture, in  such  a  manner  that  the  heat  generated  by  gradual  com- 
bustion is  absorbed  in  the  so-called  nascent  state  in  consequence 
of  a  corresponding  expansion,  i.e.,  by  mechanically  cooling  off 
the  gases,  so  that  the  period  of  combustion  is  going  on  constantly 
isothermally.  It  is  evident  that  the  fuel,  in  order  to  fulfil  that 
condition,  must  be  changed  in  its  physical  composition  to  a  gas- 
eous, liquid,  or  powdery  form/'' 

"That  is  to  say,  that  through  the  combustion  and  during  the 
same,  no,  or  a  relatively  small,  increase  of  temperature  is  caused,  an 
idea  which  seems  to  be  absurd  after  having  heretofore  always 
effected  the  increase  in  temperature  by  the  combustion  and  during 
the  same." 

So  far  Diesel,  even  after  the  experimental  stage  of  his  engine 
had  passed.  It  is  quite  evident  that  to  approximate  this  isother- 
mal combustion,  it  cannot,  after  ignition,  be  left  to  itself,  but 
must  be  externally  regulated  to  maintain  the  proper  relation 
between  temperature,  pressure,  and  volume,  as  Diesel  himself 
says.  In  the  Diesel  engine  as  at  present  constructed  no  such 
control  is  attempted,  and  it  is  hence  difficult  to  see  how  isothermal 
combustion  can  be  realized.  Giildner,  from  indicator  diagrams 
published  by  Schroter  in  1897,  accordingly  found  upon  analysis 
that  there  was  a  decided  temperature  increase  along  the  combustion 
line.  The  airwas  compressed  to  600  degrees  Centigrade  (1132  degrees 


106 


INTERNAL  COMBUSTION  ENGINES 


Fahrenheit).  At  the  full  cut-off  this  had  increased  to  about  1500 de- 
grees Centigrade  (2732  degrees  Fahrenheit),  and  due  to  after-burn- 
ing the  maximum  temperature  was  about  150  degrees  Centigrade 
(270  degrees  Fahrenheit)  higher  than  this.  The  mean  temperature 
of  the  four  strokes  was  about  500  degrees  Centigrade  (932  degrees 
Fahrenheit).  This  in  spite  of  the  fact  that  the  combustion  line 
looked  isothermal.  In  this  case  the  maximum  temperature  was 
2^  times  that  at  the  end  of  compression.  The  temperatures  thus 
realized  are  higher  than  those  found  in  engines  using  constant- 
volume  combustion,  in  spite  of  claims  to  the  contrary. 


FIG.  4-17. 

Fig.  4-17,  from  a  German  Diesel  engine  of  late  date,  shows  that 
the  combustion  is  much  nearer  that  at  constant  pressure  than 
anything  else.  This  is  a  step  in  the  right  direction,  as  it  can  be 
shown  that  isothermal  combustion  is  the  least  favorable  to  best 
efficiency.  (See  previous  chapter.) , 


FIG.  4-18. 

Fig.  4-18  shows  a  diagram  published  by  the  American  Diesel 
Engine  Company  as  late  as  1904  or  1905.  In  the  literature  accom- 
panying the  diagram,  the  claim  of  isothermal  combustion  is  still 
made.  The  combustion  line  certainly  has  that  appearance,  but 
data  is  unfortunately  lacking  to  analyze  the  diagram.  In  view 
of  the  fact  that  the  control  of  combustion  in  this  engine  has  not 
changed  very  materially  since  1897,  it  is  safe  to  assume  that  the 
combustion  is  not  isothermal,  and  it  is  perhaps  to  the  advantage 
of  the  engine  that  it  is  not. 


CHAPTER  V 

t 

THE  TEMPERATURE-ENTROPY  DIAGRAM  APPLIED  TO  THE  GAS 

ENGINE 

THE  meaning  of  the  term  "Entropy"  has  already  been  ex- 
plained in  a  previous  chapter.  It  was  also  shown  there  wrhat 
shape  various  pressure- volume  diagrams  assume  when  trans- 
formed to  a  temperature-entropy  basis.  It  is  proposed  to  show 
here  mathematically,  and  graphically  if  possible,  how  this  trans- 
formation is  made. 

Just  as  the  p-v  diagram,  by  areas  developed,  shows  the  amount 
of  work  done  during  various  events  of  the  cycle,  the  entropy 
diagram  shows  heat  interchanges  for  the  various  parts  of  the 
cycle,  and  it  is  therefore  a  valuable  aid  in  giving  an  insight  into 
the  thermal  actions  of  the  cylinder.  Unfortunately  the  labor 
connected  with  the  transposition  of  the  p-v  diagram  of  a  gas 
engine  to  the  entropy  diagram  is  considerable,  much  greater 
than  is  the  case  for  a  steam-engine  diagram.  The  reason  is  that 
in  steam  we  have  a  medium  whose  properties  are  definite  and 
unchangeable,  and  which  are  at  once  known  when  a  single  criterion 
of  the  state  of  the  vapor  is  given.  It  is  possible  also  to  construct 
entropy  tables  for  them  which  facilitate  the  work  of  transposition 
very  much.  On  the  other  hand,  a  p-v  diagram  for  a  gas  engine 
represents  factors  which  hold  for  that  diagram  and  no  other. 
Such  are  the  composition  of  the  charge,  the  specific  heats  of  the 
mixture,  the  exponents  of  the  compression  and  expansion  lines, 
etc.,  and  all  are  important  for  the  accurate  determination  of  the 
entropy  diagram.  It  may  be  said  that  for  every  different  load 
on  a  gas  engine  these  factors  differ,  and  they  will  even  change 
with  accidental  variation  in  engine  operation  at  the  same  load. 
Hence  the  construction  of  entropy  tables  for  gas  mixtures,  while 
possible,  would  be  of  use  only  when  the  conditions  of  operation 

107 


108  INTERNAL  COMBUSTION   ENGINES 

happened  to  fit  the  conditions  which  were  assumed  in  the  com- 
putations of  such  tables.  That  would  not  often  be  the  case. 
Even  a  closely  mathematical  transformation  of  the  p-v  to  the 
entropy  diagram  is  subject  to  errors,  which  make  many  authori- 
ties skeptical  as  to  the  real  value  of  the  diagram.  These  errors 
may  be  grouped  under  two  heads  : 

1.  Errors  due  to  transformation,  that  is,  errors  due  to  incor- 
rectly measuring  pressures  and  volumes  from  the  p-v  diagram, 
and  mathematical  errors  of  computation.     All  these  may  be  kept 
below  the  required  limit  by  sufficiently  careful  work.     The  orig- 
inal p-v  diagram  should  be  carefully  enlarged  and  the  measure- 
ments taken  from  this.     The  larger  the  scale,  the  better. 

2.  Errors  due  to  assuming  specific  heat  constant  with  chang- 
ing  pressure   and   temperature.      How   far   this   assumption   is 
justified  will  be  shown  in  a  later  chapter.     We  know  that  there 
is  a  variation,  but  the  law  is  not  definitely  known  for  composite 
gases,  as  CO2,  and  hence  our  assumption  of  constant  specific  heat 
results  in  a  distorted  entropy  diagram.     But  this  assumption  is 
the  best  we  can  make  with  our  present  knowledge. 

It  should  be  clear  from  the  above  that  a  strictly  graphical, 
and  therefore  time-saving,  method  of  constructing  the  entropy 
diagram  is  out  of  question.  The  greatest  stumbling  block  to  the 
general  applicability  of  such  a  method  is  apparently  the  variation 
of  the  specific  heat  with  variation  in  composition  of  the  charge. 
One  of  the  best  graphical  methods  assumes  that  the  value  of 

C 

—  —  v-~-  is  always  equal  to  2.45  for  the  perfect  gases.     This  law, 


however,  appears  to  hold  only  for  such  gases  as  H,  O,  N  and  CO, 

m, 
C 


C 
whose  —  -  is  close  to  1.41.     For  gases  like  superheated  steam,  or 

Cv 


CO2  the  factor  is  considerably  higher.     Hence  the  value  of— 

Lp  —  t/ 

at  least  should  be  fairly  accurately  computed  even  in  using  this 
graphical  construction,  the  method  for  which  will  be  explained 
later  on. 

Another  point  that  should  be  mentioned  is  the  fact  that  but 
few  gas  engine  trials  are  sufficiently  elaborate  to  furnish  enough 
data  for  the  mathematical  determination  of  the  entropy  diagram. 
The  following  data  should  be  known: 


THE  TEMPERATURE-ENTROPY  DIAGRAM  109 

1.  Composition  and  weight  of  fresh  charge  and  burned  gases. 

2.  Heating  value  of  the  fuel  and  of  the  charge. 

3.  Temperature  at  some  point  of  the  p-v  diagram,  preferably 
at  end  of  suction  stroke. 

4.  Stroke  and  clearance  volume. 

5.  Index  of  the  expansion  and  compression  lines. 

In  the  following  will  be  given  first  the  mathematical  basis  for 
the  entropy  diagram;  this  will  be  followed  by  the  actual  con- 
struction of  such  a  diagram,  and  finally  it  will  be  shown  how  the 
same  diagram  can  be  obtained  in  a  way  mainly  graphical. 

The  following  mathematical  exposition  is  due  to  Grover.*  His 
demonstration  of  the  general  expression  for  entropy  of  a  gas  is 
especially  clear. 

Let  H  =  quantity  of  heat  in  thermal  units  added  to  or 
subtracted  from  a  mass  of  gas. 

Cv  =  specific  heat  at  constant  volume. 
Cp  =  specific  heat  at  constant  pressure. 
T  =  absolute  temperature. 

p  =  absolute  pressure  in  pounds  per  square  foot. 
v  =  volume  in  cubic  feet. 
,7  =  mechanical  equivalent  of  heat. 
<j>  =  entropy. 
It  may  be  remembered  from  the  statements  in  Chap.  II  that 


When  heat  is  supplied  to  a  mass  of  gas  the  volume,  pressure, 
and  temperature  of  the  gas  may  vary  simultaneously.  Hence  we 
may  write  the  energy  changes  occurring  under  the  conditions  in 
the  following  general  terms,  following  Grover: 

Additional  internal  f  External  effect  of  1 


Addition  of  heat 
may  produce 


energy  of  the  gas  in- 
volving rise  of  tern-    \  -|- 
perature. 


work  done  by  the 
gas  expanding  be- 
tween its  contain- 


ing walls. 
With  the  notation  above  given  we  may  write  this 


+  ySF  (2) 


*  Grover,  Modern  Gas  and  Oil  Engines. 


110  INTERNAL  COMBUSTION  ENGINES 

but  2?  =  R  =  J(C,  -  Cy  (3) 

/TT 

hence  p  =  J(CP  —  Cv}-±-  (4) 

v 

Substituting  (4)  for  p  in  equation  (2) 

&« 

(cv  -  c»>  r-^  (5 

and  r      S*  =  f  =C.-^  +  <C,  -  C.)-^    ,    |     '  ((j) 

which  is  the  general  equation  for  entropy  of  a  gas. 

Now  heat  may  be  added  to  or  subtracted  from  a  body  of  gas 
under  three  conditions:  (a)  at  constant  volume;  (6)  at  constant 
pressure;  or  (c)  pressure  and  volume  may  change  at  the  same 
time. 

Case  (a).   Change  of  heat  at  constant  volume. 
Under  this  condition 


-    0 


and  we  shall  have  from  (6)  simply 

,,      SH      '    ST 

ixf  -  Y=  C*-T  (8) 

Case  (b).   Change  of  heat  at  constant  pressure. 
From  pv  =  RT 
and  pto  =  R*T 
we  may  derive 

RT~  =  RST 

v 

Sv     8T 

V=Y  (9) 

c\ 

Substituting  this  value  of  --  in  equation  (6)  we  have 


_       - 
=  Y  "  LPT  (10) 

Case  (c).    Simultaneous  change  of  pressure  and  volume. 


THE  TEMPERATURE-ENTROPY  DIAGRAM  111 

For  this  condition  we  may  write 

pvn  =  p1vin  =  constant  (11) 

From  pv  =  RT,  we  have 


(12) 

Substituting  (12)  in  (11) 

RTv""1  =  constant  (13) 

Differentiating  (13) 

STV"1  +  T  (n-1)  vn~2  &v  =  0  (14) 

S7V-1  =  -  T  (n-1)  vn~2  8v  (15) 

Divide  by  vn~* 


Y~     'VY  '}T(n-l) 

-*T(cv  1°*-°^ 


n-  I 


J 


or  _8v_  ST 

~7~  ~T(n-l)  (17) 

Substituting  (17)  in  general  equation  (6) 


T      '*T  "T(n-l)  (18) 

To  simplify  this,  write 


and  substitute  this  value  of  Cf  in  (18) 


VT    n-lj  (20) 

Restating  these  results  we  have 
Volume  Constant 


112  INTERNAL  COMBUSTION  ENGINES 

and  entropy  change  is 

Pressure  Constant 


,.      ,, . (22) 

Change  of  volume  and  pressure,  according  to  pv"    =  constant. 


and  /    _    \         7* 

<k-^  =  ag— Qioge^  (23) 

As  already  stated,  it  is  not  easy  to  obtain  tests  which  give 
sufficient  data  to  construct  the  entropy  diagram.  One  of  the 
most  complete  was  a  test  by  Brooks  and  Steward,  made  twenty- 
three  years  ago  at  Stevens  Institute.  The  engine  tested  developed 
about  7  horse-power  on  illuminating  gas.  Although  several  of 
the  operating  conditions  of  this  test,  especially  the  low  compres- 
sion pressure  of  43.5  pounds,  do  not  represent  modern  practice, 
the  complete  data  furnished  makes  ,this  test  well  adapted  to  the 
purpose  in  view. 

I.  MATHEMATICAL   CONSTRUCTION   OF   THE   ENTROPY   DIAGRAM. 

All  pressures  and  temperatures  are  absolute. 
1.   Composition  and  weight  of  fresh  charge  and  burned  gases. 
(a)  Composition  of  illuminating  gas  by  volume. 

H  CH4  N  C3H6  CO  O      H3O 

.395          .373          .082          .066          .043          .014      .027 

From  this  we  compute  the  weight  of  a  standard  cubic  foot  of 
gas  at  .03882  pounds. 

(6)  Ratio  of  air  to  gas  by  volume   =    6.63,  from  test. 
Ratio  of  air  to  gas  by  weight       =  13.78,  from  test. 

(c)  Volume  and  weight  of  the  various  gases  per  stroke. 

The  figures  are  given  in  the  report  in  metric  units.  They  are 
transposed  as  follows: 


THE   TEMPERATURE-ENTROPY  DIAGRAM  113 

For  one  charge  stroke  the  engine  takes  the  following  volumes: 

1.40  liters  of  gas  \  f  .0494  cu.  ft.  of  gas  \ 

Ut295°C.  --3  I  at  533°  F. 

9.25  liters  of  air    )  (  .3265  cu.  ft.  of  air  ) 

7.94  liters  of  burned  gas  at  683°  C.=  .2805  cu.  ft.  burned  gas  at 

1261°  F. 
Now,  — 

.0494  cu.  ft.  of  gas  at  533°  F.  =  .0457  cu.  ft,  at  493°  F. 

which  weigh      .00178  Ib. 
.3265  cu.  ft.  of  air  at  533°  F.  -  .3020  cu.  ft.  at  493°  F. 

which  weigh      .02437  Ib. 
.2805  cu.  ft.  burned  gas  at  1261°  F.  =  .1091  cu.  ft.  at 

493°  F.  which  weigh      .00862  Ib. 
Hence  total  weight  of  charge  =  .03477  Ib. 

(d)  Composition  of  exhaust  gases. 

From  above  composition  of  illuminating  gas  the  theoretical 
ratio  of  air  to  gas  by  volume  is  5.93.     Hence  excess  coefficient  is 

if/  |q  I  IS-'--          ! 

The  weights  of  the  products  of  combustion,  therefore,  from 
1  pound  of  gas  will  be 

1.940  Ib.   CCU 

}•  from  gas  burned. 
1.7401b.  H2O) 

.006  Ib.  N         originally  in  gas. 
9.490  Ib.  N         from  air  used  for  combustion. 
1.120  Ib.  N      J 

r  from  excess  air. 
.340  Ib.  O      ) 

From  this  the  composition  per  cent  by  weight  of  the  exhaust 
gases  is 

CO2          H2O  N  O 

13.18        11.82  72.70          2.30 

(e)  Cp  and  Cv  for  the  fresh  charge  and  the  exhaust  gases  are 
found  by  computation  to  be  as  follows: 


114  INTERNAL  COMBUSTION   ENGINES 

For  fresh  charge,  Cp    =  .265,  Cv  =  .191,  ^  =  y  =  1.39 
For  burned  gases,  G\    =  .268,  Cv  =  .196,  ^  =  y  =  1.37 

™  I     ,„. 


,240 


230 


170 


C    .  V  >lum« .  Cubic  Fe  it 
0       .04      .08     .12      .10       .20     .24,      .28     .32      ^36      JO     & 


3440 


•31804  323.J 


KiC5-  rl,T85 

1058- 

1005 


te-  Figure 
indicH 


\ 


diagra 


Tem'p.  *F 


.50      .00       .6^     408      32      .70 


FIG.  5-1. 

2.  Heating  value  of  the  fuel  is  found  by  computation  to  be 
617.5  B.  T.  U.  per  cubic  foot. 

Heating  value  of  the  charge  as  computed  for  the  weight  of 
gas  in  a  charge  is  29.06  B.  T.  U. 


THE   TEMPERATURE-ENTROPY  DIAGRAM 


115 


3.  The  absolute  pressure  at  the  end  of  the  suction  stroke, 
see  diagram,  Fig.  5-1,  was  12.3  Ib.  Brooks  and  Stewart  calcu- 
lated the  absolute  temperature  for  the  same  point  at  739  degrees 
Fahrenheit.  By  using  the  equation 


T       Tl 

temperatures  were  computed  for  various  points  around  the  cycle 
as  indicated  on  the  card.  In  Fig.  5-1  the  full  line  shows  the  actual 
card,  enlarged  from  the  original  of  Brooks  and  Stewart,  while  the 
broken  line  indicates  the  ideal  cycle  which  receives  the  same 
amount  of  heat. 

4.    Stroke  volume  =  .460  cu.  ft. 

Clearance  volume      =  .280  cu.  ft. 


Total  volume  =  .740  cu.  ft. 

5.    Index  for  expansion  and  compression  lines. 

The  index  of  the  ideal  card  is  1.39  for  the  compression  and 
1.37  for  the  expansion  line  as  computed  under  (1,  e).  For  the 
real  diagram  it  is  often  found  that  the  index  is  not  a  constant  for 
the  entire  line.  For  that  reason  each  line  should  be  divided  into 
a  number  of  parts  and  the  index  determined  for  each. 


FIG.  5-2. 

The  method  of  doing  this  is  as  follows:  To  determine  the 
index  between  any  two  points  a  and  b  on  the  expansion  or  com- 
pression line,  Fig.  5-2,  find  the  volumes  and  absolute  pressures 


116  INTERNAL  COMBUSTION  ENGINES 

for  each  point  from  the  diagram.     Then  the  exponent  or  index 
in  the  equation  pvn  =  constant  is 

log  pa  -  log  ph 

n<i-b  =~i  —         —  i  — 

log    Vb   —  log    Va 

In  the  case  of  the  diagram  under  discussion  this  method  when 
applied  to  the  expansion  and  compression  lines  gave  the  follow- 
ing results: 

Expansion   line 

Part  of  line  Index 

54.6  to    68.2  Ib.  n  =  1.433 

68.2  to    87.6  Ib.  -  1.384 

87.6  to  116.0  Ib.  =  1.281 

116.0  to  135.0  Ib.  =  1.149 

Compression  line 

Part  of  line  Index 

12.3  to  18.1  n  =  1.390 

18.1  to  23.0  *  1.390 

23.0  to  30.0  =  1.351 

31.0  to  43.5  =  1.272 

We  are  now  ready  to  make  the  entropy  computations.  Since 
entropy  difference  from  point  to  point  and  not  absolute  value  of 
entropy  is  the  important  thing,  we  may  call  the  entropy  at  any 
convenient  point  in  the  cycle  equal  to  zero.  We  therefore  assume 
the  entropy  at  the  end  of  the  suction  stroke  equal  to  0,  and  we 
will  call  the  entropy  difference  between  any  two  points  =  <£t  — 

$2  ^  <£• 

Ideal  Card.     (See  temperatures  in  Fig.  5-1.) 

1.  Compression  line  is  adiabatic,  hence  entropy  =  0  also  at 
the  end  of  this  line. 

2.  Combustion  line. 


'  =    -3166 


3.    Expansion  line  is  adiabatic,  hence  entropy  is  not  changed 
and  =  .3166  at  end  of  this  line. 


THE  TEMPERATURE-ENTROPY  DIAGRAM 


117 


4.    Discharge  line. 

<£  =  ^12-3  -  <£  62.8=  -196 


739 


-  -.3166 


This  locates  the  end  points  of  the  combustion  and  discharge 
lines  in  the  entropy  diagram.  But  these  lines  are  curves  and 
hence  several  intermediate  points  on  each  line  should  be  deter- 
mined by  similar  computations.  The  diagram  obtained  by 
plotting  temperatures  and  volumes  of  entropy  above  computed 
is  shown  in  broken  line  in  Fig.  5-3. 


5000 
5200 
4800 
4400 
4000 
3600 
3200 
2800 
2400 
2000 
1'GOO 
1900 

F 

/, 

/ 
/ 

r     1 
1 

X 

1 
I 

^ 

rf 

1 
J 

-ri.. 

/ 

\ 

x'' 

f/ 

5 
H 

EX 

x 

n 

/ 

xx 

§ 

XI 

^s 

ft 

2 

^ 

^ 

x^ 

^x 

^ 

^ 

^^t* 

^X^ 

^x^ 

.x—  • 

xx- 

^ 

^^^- 

+^ 

x-x* 

800 
400 

AK 

***^ 

*~~~- 

.-  — 

—  -~ 

isq 

iii. 

3 

B1 

U. 

•I 

^ 

Ent 

ropy 

! 

7, 

.04    .06     .08.     .10     .12.    .14.     .16     .18     .20     .22.     .24     .20     .26     .3 

FIG.  5-3. 

Actual  Card.  For  the  actual  card  we  proceed  in  an  exactly 
similar  manner,  using  equations  (21),  (22),  or  (23)  as  the  case 
demands.  The  computations  are  given  below  in  detail.  No 
further  explanation  seems  necessary,  except  perhaps  for  the  case 
where  both  pressure  and  volume  change  but  the  index  of  the 
curve  is  not  known.  Then  none  of  the  equations  given  directly 
apply. 

Take  the  case  of  the  diagram,  Fig.  5-4.  To  determine  the 
entropy  at  point  a,  find  entropy  at  point  b,  using  equation  (21), 
and  then  add  the  entropy  from  6  to  a  as  computed  from  equation 
(22).  Similarly  for  the  point  c  on  the  exhaust  line.  Prolong 


118 


INTERNAL  COMBUSTION  ENGINES 


the  expansion  line  and  determine  the  entropy  at  d  by  equation 
(23)  (index  n  must  be  known).  Then  subtract  from  this  the 
entropy  change  due  to  the  drop  in  temperature  from  d  to  c,  ac- 
cording to  equation  (21). 


L_ 


FIG.  5-4. 


The  following  are  the  computations  in  detail 


Entropy 

at 

Press.    Temp. 

absolute 

12.3      739 

18.1      817 

23.0      867 

926  = 


1.351  -  1.390 


assumed  =  0 
adiabatic  =  0 
adiabatic  =  0 
926 


43.5    1005 


60.0 
80.0 
120.0 
140.0 
151.3 
135.0 


1365 
1816 
2740 
3235 
3615 
3560 


H6.0  3820. 

87,  3290  = 
68.2 


Total  Entropy 

0 
0 
0 

-.0014 
-  .0080 


.196  loge  HM-  -268  loge  ffff  =  +  . 0591  +.0511 

.196  loge  fHf  =  +  .0559  +.1070 

.196  loge  f  Jfl  +  .268  loge  f f  f i  =  +  .0807  +  .1877 

.196  loge  f  Mt  +  -268  loge  MM  =  +  .1 140  (above  80  Ibs.)  +  .2210 
.196  loge  ffff  +  .268  loge  IfH  =  +  -1376  (above  80  Ibs.)  +  .2446 
.196  loge  fM£  +  .268  loge  MM  =  +  -1425  (above  80  Ibs.)  +  .2495 
1  o»7n  QKon 

=  +  .0029  +  .2524 


+  .0033 
-.0005 


+  .2557 
+  .2552 


THE  TEMPERATURE-ENTROPY  DIAGRAM  119 


54.6    2860  =  .196—  — £33^ loge  3070    =~-0019  +.2533 

4,727SO=,96l^»og^    =-.0007 


47.0    2640  =  .196^^=-3-  -  loge  |^-  .196  log^  _  -  .0053,  +  .2463 

34.5  2010  =  .196l^4r_L3Iologe|^_.1961oge|6|o__  0566)  +  196Q 

20..5     1230  =  .196  I^l^log«fl2  _  ,196  log|H  _  _  1550>  +  -0976 

12.3      739  -  .196  loge  Tl||  -  -  .0978  -  .0002 

Having  thus  worked  around  the  cycle,  the  error  seems  to  be 
very  slight  in  view  of  the  fact  that  the  exponent,  n,  for  the  pro- 
longed expansion  line  has  been  assumed  =  1 .433. 

Plotting  these  values  of  entropy  and  temperature  finally. re- 
sults in  the  diagram  shown  in  full  line  in  Fig.  5-3. 

INTERPRETATION  OF  THE  ENTROPY  DIAGRAM,  FIG.  5-3. 

In  order  to  evaluate  the  diagram  it  is  necessary  to  know  the 
number  of  heat  units  per  square  inch.  This  is  most  easily  ob- 
tained by  multiplying  one  inch  of  temperature  scale  by  one  inch 
of  entropy  scale,  and  then  multiplying  the  result  by  the  charge 
weight  per  cycle,  since  the  entropy  diagram  is  drawn  for  1  pound 
of  charge  weight.  In  this  case  we  have: 

Value  of  1  square  inch  in  B.  T.  U.  =  800  X  .04  X. 03477=  1.113. 

The  individual  areas  of  the  original  diagram  were  next  gone 
over  with  a  planimeter,  and  after  multiplying  each  area  by  the 
square  inch  equivalent,  the  results  were  as  follows: 

%of 
B.  T.  U.  Total  Heat 

1.  Heat  received  during  explosion,  area  a  A  Bba 18.086          62.24 

2.  Heat  received  during  expansion,  area  b  B  C  D  d 1.002  3.44 

3.  Total  heat  received,  as  shown  by  diagram 19.088  65.68 

4.  Total  heat  supplied  as  calculated  (see  footnote) 29.316 

5.  Difference  in  heat  loss  to  Jacket  and  Radiation  =  area 

dDC  BE  F  fd    10.228  34.89 

6.  Heat  loss  to  exhaust,  area  gG  Ddg 13.422  45.78 

7.  Heat  loss  during  compression,  area  a  A  G  g  a 233  .79 

8.  Total  heat  lost  per  cycle 23.883  81.46 

9.  Indicated  work,  area  A  BC  DG  A 5.431  18.54 

29.314         10000 


120  INTERNAL  COMBUSTION    ENGINES 

The  above  results  do  not  agree  with  those  of  Brooks  and 
Stewart  for  the  same  test.  Their  results  are  given  in  the  follow- 
ing table: 

Heat  in  indicated  work    ...........    17.0  per  cent. 

Heat  loss  in  hot  gases  .............    15.5  per  cent. 

Heat  loss  in  water  jacket  ..........   52.0  per  cent. 

Heat  loss  in  radiation  .............    15.5  per  cent. 

Total  ..............  ..........  100.0  per  cent. 

The  agreement  as  regards  indicated  work  is  fair.  The  rest 
of  the  figures  of  Brooks  and  Stewart  are  abnormal,  in  that  the 
radiation  loss  is  as  large  as  the  exhaust  loss,  and  in  that  the 
jacket  water  loss  is  much  too  large.  Brooks  and  Stewart  them- 
selves admit  that  the  jacket  water  loss  was  not  accurately  deter- 
mined. For  that  reason,  too,  the  radiation  loss  cannot  be  found 
separately  in  the  entropy  analysis  above  given.  If  the  jacket 
water  loss  had  been  accurately  found,  item  5  in  the  above  analysis 
could  have  been  separated  into  jacket  water  and  radiation  loss. 

NOTE.  —  This  quantity  is  greater  than  the  latent  heat  energy  in  the  gas 
=  29.06  B.  T.  U.  per  cycle,  by  the  heat  equivalent  ofc  the  area  A  X  g  a  = 
.256  B.  T.  U. 

II.    GRAPHICAL  CONSTRUCTION  OF  THE  ENTROPY  DIAGRAM 
The  graphical  method  to  be  described  is  due  to  Prof.  H.  T. 
Eddy,  and  is  by  him  explained  in  the  Transactions  of  the  Ameri- 
can Society  of  Mechanical  Engineers,  Vol.  21,  p.  275.     It  is  based 
upon  the  following  considerations: 

Equation  (6),  p.  110,  after  integration  may  be  written: 

Entropy  difference  </>  =  <£t  -  4>2=  Cv  loge  -1  +  (CP-  Cv)  logZ1      (24) 

1  2  *  2 

Dividing  equation  (24)  by  (Cp  —  Cv)  we  have 


The  problem  then  resolves  itself  into  rinding  graphical  represen- 
tation for  the  quantities 

-^  log.  £  and  log.  J» 

Uf-L't)  ^2  '2 

The  construction  divides  itself  into  two  main  parts  : 

1.    The  change  of  the  pressure-  volume  diagram  into  a  tempera 
ture-volume  diagram,  and 


THE   TEMPERATURE-ENTROPY  DIAGRAM  121 

2.    The  change  of  the  temperature-volume  diagram  so  ob- 
tained into  a  temperature-entropy  diagram. 


Actual  p-V  Diagram 


Ideal  " 

Actual  T-V 

I'deal  " 

Actual  Entropy 

Ideal 


Hi  |.144        i       .I'.rj  ;      |      1.2-10 

vi.VolinieTcub"idFeeti     I 


0        .04      ,08      .12      .10      .20      .24      .28     .32      .30      .40     .44      .48      .52     .50      .QO      .04 


122  INTERNAL  COMBUSTION  ENGINES 

1.  In  Fig.  5-5  the  actual  and  ideal  p-v  diagrams  of  Fig.  5-1 
have  been  reproduced.  Choose  any  convenient  volume  ordinate, 
in  this  case  V  =  .38  cu.  ft.  has  been  taken,  and  from  the  points  of 
intersection  of  the  various  pressure  levels  with  this  ordinate 
draw  straight  lines  through  the  origin.  These  straight  lines  are 
constant-pressure  lines  in  a  temperature-  volume  field.  Thus  the 
.line  A  B  in  this  case  is  the  60  pounds  constant-pressure  line.  To 
see  the  reason  for  this  consider  the  general  equation 


This  may  be  written 

v  _R        T  _p 
T~p  >°Tv~R 

rn 

But  -  is  the  tangent  of  any  given  angle,  BAG,  and  hence  ^  is 
v  H 

constant  for  any  point  along  A  B.  The  same  holds  for  any 
straight  line  drawn  through  any  other  pressure  level. 

Next,  to  construct  the  temperature-volume  diagram,  con- 
sider any  pressure  level  as  E  F  =  100  Ib.  This  cuts  the  real 
diagram  in  the  points  a  and  6.  At  a  and  6  erect  perpendiculars 
until  they  intersect  the  constant-pressure  line  =  100  Ib.  in  the 
points  a'  and  b'.  These  will  be  two  points  in  the  temperature- 
volume  diagram.  In  the  same  manner  the  entire  diagram  may 
be  outlined.  The  temperature  scale,  which  up  to  this  point  has 
been  arbitrary,  may  next  be  determined.  We  know  that  G,  the 
lowest  point  on  the  temperature  diagram,  must  represent  the 
temperature  in  the  cycle  at  the  end  of  the  suction  stroke  = 
739  degrees  Fahrenheit.  This  at  once  determines  the  tempera- 
ture scale. 

2.    To  obtain  the  graphical  representation  of  the  expression 

y 
\oge  —  r1  choose  any  convenient  horizontal  line  as  the  zero.  In 

*j 
this  case  the  line  A  C  has  been  taken.  With  A  as  a  center  and 

any  radius  AX,  draw  the  arc  XY  to  cut  any  convenient  line,  as 
A  B,  passing  through  the  origin.  From  Y  draw  the  perpendicu- 
lar YX'.  Again  with  A  as  a  center  and  AX'  as  radius,  draw  the 
arc  X'Y'  to  intersect  with  A  B,  and  draw  the  perpendicular  Y' 
X".  Where.  these  perpendicular  lines  YXl  and  YVX"  cut  any 
successive  pair  of  equidistant  horizontal  rulings  will  be  found  two 


THE  TEMPERATURE-ENTROPY  DIAGRAM  123 

points  on  the  required  curve.  The  horizontal  rulings  chosen  in 
this  case  are  marked  serially  on  the  ordinate  V  =  .22  cu.  ft. 
Thus  m  and  n  are  two  points  on  the  curve  MN  sought.  It  is 
evident  that  the  intersections  of  perpendiculars  YXf  and  Y'X" 
with  any  other  two  successive  horizontal  rulings  might  have  been 
chosen  as  two  points  on  the  curve.  This  would  have  resulted 
merely  in  moving  the  curve  bodily  up  or  down  on  the  field,  the 
shape  would  have  been  exactly  the  same.  For  the  same  reason 
it  is  immaterial  whether  the  line  A  C  or  any  other  horizontal  line 
is  used  as  the  base  of  construction.  The  resulting  curve  is  in 
any  case  asymptotic  to  the  vertical  line  V  =  0.  Choosing  any 
other  set  of  equidistant  horizontal  rulings,  nearer  together  or 
further  apart,  has  the  effect  of  making  the 'curve  rise  slower  or 
faster  as  the  case  may  be.  As  will  be  seen  later  by  inspection, 
this  merely  changes  the  position  of  the  entropy  diagram  in  the 
coordinate  field  but  does  not  affect  the  final  result. 

To  prove  that  the  ordinates  of  the  curve  M  N  represent  the 

T7- 

values  of  log  — ^,  Professor  Eddy  proceeds  as  follows : 

Let  the  volume  AX  =  V0,  AX'  =  Vv  AX"  =  V2,  AXn  =  Vn. 
It  can  be  shown  by  plane  geometry  that,  with  the  construction 
used, 

_!=       2=__«_  =  Z 

or  ZV0  =  Vv  ZVt  =  V2l.  . .   "  . ! .  -ZVn_=Vn 

Hence 

7217    .  _  v     73 v    .  _  v  7"V    •  -  V 

^   v  o  ~     K2>z/Ko~     K  3     ^    v  o  ~     y  n 

Now  let  Z  =  ey  in  which  e  =  Naperian  base  =  2.7  +,  and  y  = 
distance  between  the  equidistant  horizontal  rulings  above  as- 
sumed. 

Then 

ey—  J_i    ezy—  _L?  eny  —  J_» 

v  '      ~  v   ~  v 

V  0  V  0  K  0 

and  taking  the  logarithm  of  both  sides  of  the  last  term,  we  have 
n  y  =  the  ordinate  at  any  given  volume  Vn  =  \oge  ^.  It  is 

^0 

evident  that  V0,  the  unit  of  comparison,  may  be  arbitrarily  chosen. 
The  next  step  is  to  obtain  the  graphical  representation  of  the 

C  T  T 

expression  - —  ^—  loge  ~.     Considering  the  part  loge  =i  by  itself, 

Lp  L>v  1  2  1  2 


124  INTERNAL  COMBUSTION  ENGINES 

it  is  evident  that  the  curve  representing  this  may  be  constructed 
in  the  same  manner  as  curve  M  N.  But  the  coordinates  are  in 
this  case  the  line  of  zero  temperatures,  A  C,  and  any  arbitrarily 
chosen  vertical  line,  in  this  case,  V  =  .74.  The  curve  must  be 
asymptotic  to  A  C,  but  the  choice  of  the  other  line  of  reference 
is  unrestricted  as  it  merely  moves  the  curve  bodily  to  the  left  or 
right.  In  this  case  equidistant  vertical  rulings  having  the  same 
common  distance  as  those  used  for  curve  M  N  have  been  em- 
ployed, hence  curve  0  P  is  a  duplicate  of  M  N. 

The  ordinates  of  this  curve  0  P  must  next  be  multiplied  by 

C 

the  factor  -^-'^-^  .     Professor  Eddy,  in  order  to  make  the  con- 
Cp—Cv 

struction  graphical  throughout,  assumes  that  the  value  of  this 
factor  is  2.45  in  all  cases.  The  limits  of  accuracy  regarding  this 
assumption  have  already  been  pointed  out.  It  is  probably  not 
sufficiently  accurate  for  most  cases,  and  hence  a  separate  compu- 
tation of  this  factor  is  necessary  for  every  given  case.  This  de- 
stroys a  great  deal  of  the  value  of  the  entire  method,  but  enough 
is  left  to  make  the  method  much  less  laborious  than  the  mathe- 
matical construction. 

In  the  case  under  discussion,  for  the  burned  gases, 

Cv=  .196,  and  Cp=  .268;  hence:  ~~«J        =2.72 


The  ordinates  of  the  curve  0  P  are  therefore  multiplied  by  2.72, 
giving  the  curve  marked  R  S. 

By  the  aid  of  the  curves  M  N  and  R  S,  the  entropy  diagram 
may  now  be  constructed  in  the  following  manner: 

Take  any  temperature  level  as  T  U.  This  cuts  the  tempera- 
ture-volume diagram  of  the  real  cycle  in  the  points  c  and  d,  and 

the  curve  R  S  in  e.     With  a  pair  of  dividers  determine  the  ordi- 

/         y  \ 
nate  g  h  of  the  curve  M  N,  I  logc     *  j,  corresponding  to  the  volume 

of  point  c,  and  since  this  ordinate  is  positive,  add  it  to  the  ordi- 

/     C  T  \ 

nate  /  e  (        v      loge  ..  l  )  of  the  curve  R  S.     This  gives  the  point 

\C/>—  LV  1  2/ 

e'  as  one  point  of  the  entropy-temperature  diagram.  In  the 
same  manner,  for  the  second  point  of  intersection,  d,  of  the  tem- 
perature level  T  U,  determine  the  ordinate  g'  h',  corresponding 
to  its  volume,  and  add  it  to  the  ordinate  fe  of  the  curve  R  S,  This 


THE  TEMPERATURE-ENTROPY  DIAGRAM  125 

gives  e"  as  a  second  point  on  the  entropy  diagram.  By  taking  a 
sufficient  number  of  temperature  levels,  the  entire  diagram  may 
be  closely  outlined,  as  shown  by  the  full  line. 

The  same  thing  has  been  done  for  the  ideal  temperature- 
volume  diagram,  giving  the  ideal  entropy  diagrain  indicated  in 
broken  line. 

The  last  step  in  the  construction  is  the  determination  of  the 
entropy  scale,  if  this  is  desired.  Determine  by  planimeter  the 
area  under  the  combustion  line  of  the  ideal  diagram  down  to 
the  line  T  =  0.  In  the  original  diagram  this  was  found  to  be 

28.32  square  inches.  Since  the  heat  applied  the  cycle  was  29.06 

oo  C\R 

B.  T.  U.,  the  thermal  value  of  each  square  inch  of  area  =  ^^  = 

28.  32 

1.026  B.  T.  IT.  Each  inch  of  ordinate  was  equal  to  614  degrees, 
hence  the  entropy  scale  per  inch  is  -r~  =  .00167  for  the  charge 


weight  of  .03477  pounds.     This  is  equivalent  to  an  entropy  scale 
of  .048  per  inch  for  one  pound  of  charge  weight. 

The  following  table  shows  how  closely  the  entropy  diagrams 
obtained  by  the  two  methods  outlined  agree  : 

Math.  Method      Graph.  Method 

Max.  Entropy  of  Ideal  Cycle  .  ...  .3166  .3158 

Max.  Entropy  of  Real  Cycle  .....  .2557  .2572 

The  agreement  may  be  pronounced  quite  satisfactory.  It  is 
quite  likely,  however,  that  the  lower  part  of  the  graphical  entropy 
diagram  will  show  discrepancies.  These  are  in  great  part  due  to 
the  fact  that  toward  the  lower  end  of  the  curve  R  S,  the  inter- 
sections with  the  horizontal  temperature  levels  become  less  defi- 
nite, impairing  the  accuracy.  Another  source  of  error  may  lie 
in  the  fact  that  the  compression  line  has  been  constructed  from 
the  curve  R  S,  which  was  itself  constructed  from  burned  gas 
data,  while  evidently  the  data  of  the  fresh  charge  should  have 
been  used. 


CHAPTER  VI 


COMBUSTION 

i.  The  Perfect  Gases.  —  The  perfect  gases  are  those  which 
follow  the  general  law: 

Y=R  C1) 

where 

p  =  pressure  expressed  in  pounds  per  square  foot. 

v    =  volume  in  cubic  feet. 

T  =  absolute  temperature. 

R  is  the  amount  of  work  done  by  1  pound  of  gas  when  heated 
1  degree  Fahrenheit,  the  pressure  remaining  constant  at  p 
pounds  per  square  foot.  R  is  thus  a  constant  for  any  one  gas, 
but  differs  for  different  gases. 

The  data  for  the  gases  of  most  use  in  gas-engine  practice  are 
those  of  atomic  and  molecular  weight,  density  and  weight  per 
cubic  foot.  The  following  table  gives  these  figures  for  some  of 
the  more  important  gases: 


Gas 

Atomic 
Weight 

Molecular 
Formula 

Molecular 
Weight 

Density 
Air=l 

Weight  per 
cu.  ft.  at 
29.92"  Hg 
and  32°F 

Hydrogen       

1 

Ho 

2 

0692 

.  00559 

Oxygen. 

16 

Oo 

32 

1  106 

08921 

Nitrogen  

14 

N2 

28 

.971 

.07831 

Carbon  Monoxide    . 

14 

CO 

28 

.967 

.07807 

Carbon  Dioxide  .  .  . 

14.6 

00, 

44 

1.529 

.11267 

Dry  air   

_•__ 

__ 

29* 

1.00 

.08072 

Water  vapor    

6 

H2O 

18 

.623 

.05020 

v.  Acetylene  

6.5 

C2H2 

26 

.915 

.07251 

Methane    ......... 

3.2 

CH4 

16 

.554 

.04464 

Ethylene  

4  7 

CofL 

28 

.974 

.  07809  " 

Benzol 

5  75 

C«H« 

78 

2  695 

.21758 

Alcohol  

6.50 

C,HfiO 

46 

1.601 

.  12958 

*Only  apparent  value. 


The  weight  of  a  cubic  foot  of  any  of  the  above  gases  under 
standard  conditions  may  be  found  with  sufficient  accuracy  by 

126 


COMBUSTION  127 

dividing  the  molecular  weight  of  the  gas  by  the  constant  359.* 
The  weight  of  a  cubic  foot  of  CO2  under  standard  conditions,  for 

44 

instance,   is  -—  =  0.1225   pounds,   as   computed  by  slide  rule. 


This  is  sufficiently  accurate  for  all  practical  purposes. 

To  find  the  weight  of  a  cubic  foot  of  gas  under  other  than 
standard  conditions,  the  formula 


m  rp  \6) 

1  0  *  1 

may  be  employed  for  a  change  of  either  pressure  and  tempera- 
ture separately  or  a  simultaneous  change  of  both.  The  weight  of 
a  cubic  foot  is  inversely  proportional  to  the  volume. 

2.  Combining  Weights  and  Volumes,  Combustion,  Heating 
Value,  Air  Required. 

COMBINING  WEIGHTS  AND  VOLUMES.  —  All  elements,  when 
they  do  combine,  unite  only  in  certain  fixed  proportions,  although 
there  may  be  several  proportions  for  any  given  pair  of  elements. 
Thus  carbon  forms  two  combinations  with  oxygen,  CO  and  CO2. 

The  gases  also  combine  in  definite  volume  proportions.  The 
resulting  volume  is  -either  the  sum  of  the  original  volumes  or  is 
in  a  definite  ratio  less  than  this  sum.  It  is  necessary  to  remember 
merely  that  anything  that  can  be  said  of  molecules  according  to 
Avogadro's  Law,  applies  with  equal  force  to  combining  volumes. 

Thus  take  the  combination  of  C  and  O  to  CO.  Always  re- 
membering to  use  the  combining  weights  of  the  various  elements 
we  can  write  C2  +  O2  =  2CO 

1  vol.  C  +  1  vol.  0  =  2  vols.  CO. 
Similarly,  2  H2  +  O2  =  2  H2O. 

2  vols.  H  +  1  vol.  O  =  2  vols.  H2O 
andagain 


1  vol.  C  +  4  vols.  H  =  2  vols.  CH4. 

The  elements  mostly  concerned  in  combustion  phenomena 
are  carbon  and  hydrogen,  together  with  the  compounds  carbon 
monoxide  and  the  various  hydro-carbons.  The  following  table 

*  Derived,  in  connection  with  Avogadro's  Law,  from  the  fact  that  the 
kilogramme-  volume  of  perfect  gases  is  equal  to  22.33  cubic  meters  under 
standard  conditions. 


128 


INTERNAL  COMBUSTION  ENGINES 


shows  the  combustion  formula,  also  oxygen  and  air  required,  for 
the  first  three  of  these  combustibles: 


# 

oo 

oo 

^ 

3      1 

CO 

t  *". 

^T1                  | 

. 

S3       3 

<M 

c^ 

a    o 

•g  >:'1 

O^           ^O           "^                  ^^ 

^t1                                                   T™1 

.S  °    § 

!     * 

£                * 

*}j 

2 

I 

1.1 

oo        oo        b 
t^        1>        " 

^                 rh 

w      o 

PH 

CO 

H 

S 

OOO             _: 

1 

to  'S     1 

I6  :d 

M 

-  £  ^  8  c 

^8    ^o 

C 

'S 
15 

S 

W  >  o  ^  c 

.    (N        .    CNJ 

>l  8! 

0 
O 

1    ||   1    ||   1    H        'o    || 

<N               rH 

H                         C<J 

w    8    £ 

1      8 

£           £           £                  -O 

CO            CO                    *O 

-2 

<N            C 

0                       rH 

.£? 

II              II 

1                           II 

°5 

II                  II 

1                      --                                'I 

pE 

ooo         o 

I 

=2      £ 

£                -Q 

'.B 

00  i  § 

§t^ 
10 

o 

'-i           (N 

O 

1                      1 

W      o      o          o 

rH                 T-t                i—  1                            T-H 

~  §C3 

0                0            Q 
K       8       0            " 

Oil              II                     II 

11 

II            II                  II 

ooo         o 

c5^ 

+        + 

f        + 

W      o      c 

-^                       c^ 

ll 

O        O              o 
0         0              0 

W       °       Q 

0 

o      o          o 

COMBUSTION 


129 


If  the  combustible  be  a  hydrocarbon,  the  combustion  of  the 
carbon  and  the  hydrogen  in  its  composition  can  be  treated  sepa- 
rately and  the  results  combined.  Thus  1  Ib.  of  CH4  may  be  con- 
sidered to  consist  of  |  Ib.  of  C  and  \  Ib.  of  H. 

HEATING  VALUE.  —  Every  chemical  change  is  accompanied 
by  a  thermal  change,  either  positive  or  negative,  i.e.,  either  heat 
is  given  out  or  it  is  absorbed  during  the  change.  In  the  case 
of  the  combustibles,  the  union  with  oxygen  is  accompanied  by  a 
very  decided  development  of  heat.  The  heat  given  off  when  one 
pound  of  any  combustible  is  completely  burned  is  known  as  its 
heating  value,  or  calorific  power.  It  is  to  be  noted  that  the  heat- 
ing value  of  any  combustible  is  constant,  whether  the  combustible 


FIG.  6-1.— Mahler   Bomb  Calorimeter. 

is  burned  in  oxygen,  theoretical  amount  of  air,  or  an  excess  of 
air.  The  resulting  temperature,  the  calorific  intensity  so  called, 
is,  however,  different  for  each  of  these  cases,  as  will  be  explained 
later. 

The  heating  values  of  the  simple  combustibles  like  hydrogen 
and  carbon  can  only  be  determined  by  means  of  the  calorimeter; 
that  of  a  complex  fuel,  like  hydrocarbons,  the  various  coals, 
etc.,  can  be  found  either  by  the  calorimeter  or  it  may  be  com- 
puted with  fair  accuracy  from  its  chemical  composition. 

For  solid  and  liquid  fuels  the  calorimeters  used  are  mostly 
of  the  type  of  the  Mahler  bomb,  or  the  Carpenter  calorimeter; 
for  gaseous  fuels  Junker's  gas  calorimeter  holds  the  first  place. 
The  principle  of  any  of  these  calorimeters  is  to  transmit  to  water 


130 


INTERNAL  COMBUSTION  ENGINES 


the  heat  evolved  by  burning  the  fuel  in  oxygen  or  air,  and  from 
the  temperature  rise  of  the  water  to  compute  the  heating  value. 
The  Mahler  Bomb  Calorimeter,  Fig.  6-1,  is  a  strong  steel  or 
bronze  vessel  into  which  the  finely  powdered  fuel  is  introduced, 
held  in  a  small  cup  or  crucible.  Through  the  cover  of  this  vessel 
or  bomb  two  wires  pass  which  at  their  lower  ends  are  cross-con- 
nected by  a  fine  iron  wire  which  in  turn  dips  into  the  powdered 
fuel.  The  bomb  is  charged  with  oxygen  to  a  pressure  of  about 
150  pounds.  The  oxygen  can  now  be  obtained  commercially 
prepared  in  steel  tubes,  under  pressure.  The  charged  bomb 
is  then  placed  in  a  vessel  containing  a  known  quantity  of 
water;  the  two  wires  above  mentioned  are  connected  to  a  source 


FIG.  6-2.  —  Carpenter  Coal  Calorimeter. 

of  electrical  energy,  P,  which  fuses  the  iron  wire  connecting  their 
ends  and  fires  the  fuel.  The  water  is  kept  thoroughly  stirred 
by  means  of  the  apparatus  L  K  S,  and  the  temperature  rise  is 
carefully  determined.  The  whole  apparatus  is  carefully  pro- 
tected against  radiation  by  an  outer  vessel,  A.  From  the  ob- 
served temperature  rise,  the  weight  of  water,  and  such  corrections 
as  are  necessary  for  radiation,  heat  of  fusion  of  wire,  etc.,  the 
heating  value  of  the  sample  is  easily  computed.  The  drawbacks 
of  the  instrument  are  the  labor  of  charging,  and  the  fact  that  if 
the  wire  fails  to  ignite  the  coal  all  labor  of  weighing  and  charging 
is  lost.  The  joint  at  the  top,  which  must  be  tight  against  con- 
siderable pressure,  also  often  gives  trouble.  The  Mahler  is 
applicable  to  both  solid  and  liquid  fuels. 


COMBUSTION 


131 


The  Carpenter  calorimeter,  Fig.  6-2,  is  of  a  different  type. 
The  fuel  is  powdered  and  held  in  the  cup,  22,  just  as  in  the  Mahler. 
The  coal,  however,  is  fired  by  the  heat  of  a  platinum  wire,  15, 
which  does  not  fuse,  and  is  extinguished  on  the  instant  the  coal 
fires.  No  correction  is  therefore  necessary  for  the  heat  of  the 
wire.  The  combustion  chamber,  33,  is  kept  charged  with  a 
steady  stream  of  oxygen  under  a  pressure  not  exceeding  one-half 
pound.  The  hot  gases  of  combustion  pass  up  and  down  the 
spiral  tube,  28,  and  finally  escape  at  41,  practically  at  the  tem- 


FIG.  C-3.— Junker's  Gas  Calorimeter. 

perature  of  the  surrounding  air,  the  nozzle  at  41  regulating  the 
outflow  velocity  to  produce  this  result.  The  calorimeter  is 
completely  filled  to  some  height  on  the  glass  tube,  10,  with  water  or 
kerosene  oil  so  that  the  gases  in  their  passage  heat  the  flu  id,  ex- 
panding it  up  the  tube  10.  The  amount  of  expansion  gives  a 
relative  measure  of  the  heating  value  of  the  fuel.  It  is  only  neces- 
sary to  calibrate  the  instrument,  i.e.,  to  obtain  the  amount  of 
heat  required  to  expand  the  fluid  up  the  tube  say  1  inch.  This 
is  quickly  and  accurately  done  by  using  carbon  obtained  by 


132  INTERNAL  COMBUSTION  ENGINES 

burning  and  coking  sugar.  The  calorimeter  is  subject  to  one 
correction  only,  that  for  radiation.  It  is  encased  in  a  bright 
nickel  case  to  reduce  radiation  as  far  as  possible,  but  this  can 
not  be  entirely  done  away  with.  The  correction  is  made  by 
determining  the  distance  the  liquid  level  in  the  tube  will  fall,  after 
the  fuel  sample  is  burned  out,  for  the  same  length  of  time  that 
the  fuel  burned.  Care  must  be  taken  to  have  the  temperature 
of  the  calorimeter  slightly  above  the  temperature  of  the  room  to 
start  with,  and  if  the  temperature  of  the  room  has  not  changed 
during  the  time  of  burning  and  that  of  the  determination  for 
radiation,  the  fall  in  the  water  level  is  a  true  measure  of  the  heat 
loss  due  to  radiation. 

For  gas  fuels,  Junker's  calorimeter,  Fig.  6-3,  is  usually  preferred. 
The  gas  to  be  tested  is  led  first  through  the  gas  meter  where  its 
volume  and  temperature  are  determined,  and  second  through  the 
regulator  g,  which  maintains  any  desired  gas  pressure  during  the 
determination.  It  is  burned  in  air,  with  a  burner  of  the  Bunsen 
type.  The  heat  evolved  is  transmitted  to  water,  entering  through 
the  vessel  6,  and  discharged  through  the  vessel  c,  the  gases 
escaping  at  or  near  the  room  temperature  at  K.  The  vessel  b 
maintains  a  constant  head  of  water  on  the  calorimeter.  The 
amount  of  water  flowing  is  regulated  at  e.  The  water  is  measured 
in  the  graduate  h.  The  water  of  condensation  formed  during  the 
combustion  is  caught  and  measured  at  d.  Temperatures  of  cold 
and  hot  water  are  measured  at  t  and  t'  respectively.  The  appa- 
ratus is  very  simple,  easily  set  up  in  any  desired  place,  and  the 
results  obtained  by  its  use  are  consistent  and  reliable.  Its  opera- 
tion may.be  made  continuous  by  furnishing  suitable  means  for 
measuring  the  water  flowing. 

The  heating  value  of  carbon  when  burned  to  CO2  is  now 
definitely  determined  as  14647  B.  T.  U.  per  pound  (8080  calories 
per  kilo),  that  of  carbon  to  CO  at  4429  B.  T.  U.  In  actual  prac- 
tice the  figures  14500  B.  T.  U.  for  C  to  CO2,  and  4500  B.  T.  U. 
for  C  to  CO  are  easier  to  remember  and  accurate  enough  for  most 
purposes.  The  combustion  of  C  to  CO  is  usually  known  as  the 
incomplete  combustion  of  carbon.  The  heating  value  of  the 
combustion  of  CO  to  CO2  has  been  found  to  be  4380  B.  T.  U. 

Hydrogen  gives  for  the  higher  heating  value  62100  B.  T.  U., 
and  for  the  lower  value  52230  B.  T.  U,  Hydrogen  may  burn 


COMBUSTION  133 

either  to  water  vapor,  or,  if  condensation  occurs,  to  water.  In  the 
former  case  the  heat  necessary  to  maintain  the  water  as  vapor 
is  lost,  and  hence  we  obtain  the  lower  heating  value  52230 
B.  T.  IL,  the  temperature  being  212  degrees  Fahrenheit  before 
and  after  combustion.  If  condensation  occurs,  the  heat  in  the 
water  vapor  is  recovered  and  the  higher  value  62100  B.  T.  U. 
results. 

In  gas-engine  practice  the  water  resulting  from  the  combus- 
tion of  hydrogen  almost  always  escapes  as  water  vapor,  and  hence 
it  is  usual  to  employ  the  lower  heating  value  in  computations. 

For  the  same  reason  we  distinguish  a  lower  and  higher  heating 
value  in  all  complex  fuels  containing  hydrogen  to  any  consider- 
able extent,  and  always  use  the  lower  value  in  compu- 
tations. 

If  no  direct  determination  of  the  heating  value  of  a  complex 
fuel  can  be  made  by  means  of  a  calorimeter,  the  heating  value 
can  in  most  cases  be  found  with  fair  accuracy  by  computation, 
provided  the  chemical  analysis  of  the  fuel  is  known. 

In  the  case  of  hydrocarbons  the  statement  of  its  chemical 
formula  gives  at  the  same  time  the  weight  proportions  of  its 
chemical  composition.  The  computation  of  the  heating  values 
of  the  hydrocarbon  groups  CnHw  and  CnH2w  may  be  based  upon 
the  following  considerations: 

C  H    contains  n  atoms  of  C  and  n  atoms  of  H.     Hence  the 

H        H 

gram-molecule  weighs  12n  +  n  =  I3n  grams.  Now  1  gram  of  C 
develops  32.29  B.  T.  U.,  and  1  gram  of  H  115.15  B.  T.  U.  lower 
heating  value.  The  heating  value  of  CWHW  is  therefore 

(12  X  32.29)  n  +  (1  X  115.15)  n  =  ^  R  T  n 

(U   -f-    1)  71 

This  reduces  to: 

Lower  heating  value  of  CMHW  =  17540  B.  T.  U.  per  Ib. 

CwH2n  contains  n  atoms  of  C  and  2n  atoms  of  H,  one  gram- 
molecule  therefore  weighs  14n  grams.  The  lower  heating  value 
of  this  family  of  hydrocarbons  is  therefore  generally 

(12  X  32.29)  n+  qx  115.15)  2n  =  ^  R  T   ^  p 
=  20016  B.  T.  U.  per  Ib. 


134 


INTERNAL  COMBUSTION  ENGINES 


It  should  be  remembered,  however,  that  these  formulae  give 
approximate  results  only. 

Slaby,  quoted  by  Giildner,*  in  his  Calorimetric  Investigations, 
gives  a  formula  based  upon  experience  for  heavy  hydrocarbons, 
according  to  which: 

Lower  heating  value  =  1000  +  10500  y  calories  per  cubic 
meter,  where  y  =  weight  of  a  cubic  meter  of  the  gas  in  K  g  s. 

In  English  units  this  formula  would  be: 

Lower   heating   value  = 

[112  +  18880  y]    B.  T.  U.    per   cubic  foot,  (3) 

the  cubic  foot  being  under  standard  conditions,  29.92  inches  Hg 
barometer  and  32  degrees  Fahrenheit,  and  y  =  weight  of  a  cubic 
foot. 

The  following  table  of  heating  value  of  hydrocarbons  is  taken 
from  Giildner,  the  figures  being  transposed  to  English  units. 
The  last  two  columns  show  for  purposes  of  comparison  the  values 
as  computed  by  Slaby's  formula  and  the  approximate  formulae 
first  given: 

HEATING  VALUES  OF  HYDROCARBONS 


Weight  of 
cu  ft 

Higher 

Lower  Heating 
Value 

Lower 
Heating 
Value  per 

Lower 

Heating  Value 

in  Ibs. 
Standard 

air=l 

Value 
per  lb. 
B.  T.  U. 

per  lb. 
B.  T.  U. 

percuft. 
3.  T.  U. 

cu.  ft 
Slaby's 
formula 
B.  T.  U 

Formula 
per  cu.  ft. 
B.  T.  U. 

CH4    .. 

.04464 

.554 

23842 

21385 

952 

952 

C2H2  .  . 

.07251 

.915 

21429 

20673 

1499 

1479 

1272 

C2H4  .  . 

.07809 

.974 

21429 

20025 

1564 

1584 

1562 

C2H6  .  . 

.08329 

1.0367 

22399 

20434 

1700 

1682 

C3H4  . 

.11157 

1.3819 

20992 

20009 

2232 

2238 

C3H6  .  . 

11699 

1,4512 

21224 

19820 

2317 

2318 

2341 

C3H8  .  . 

12256 

1  .  5204 

21825 

20039 

2455 

2424 

C4H8.. 

15599 

1.9349 

20912 

19508 

3032 

3055 

3120 

In  the  case  of  the  liquid  hydrocarbons,  the  crude  oils  and 
their  distillates,  it  is  usual  to  compute  their  heating  value  directly 
from  the  chemical  composition.  Thus  the  lower  heating  value 

*  Giildner,  Entwerfen  und  Berechnen  der  Verbrennungsmotoren,  2d  ed., 
p.  581. 


COMBUSTION  135 

of  a  Pennsylvania  crude  oil  containing  C  84.9  per  cent,  H  13.7 
,  per  cent,  O  1.04  per  cent,  would  be 

=  14500  C  +  52230  (ft-  ^]  (4) 

V         °/ 

-[14500  X  .849]  + 1~  52230  (.  137  -'-^Vl 

L  V  o    /  J     .   , 

=  12310  +        7102 

=  19412  B.  T.  U. 

The  determination  of  the  heating  value  of  this  oil  by  means  of 
the  calorimeter  gave  19210  B.  T.  U.,  a  difference  of  1.05  per  cent 
between  this  and  the  computed  value. 

In  many  instances,  however,  the  agreement  is  not  as  close, 
and  it  should  therefore  be  made  a  general  rule  to  obtain  actual 
calorimeter  determinations  whenever  possible,  and  to  resort  to 
computation  only  when  unavoidable. 

Solid  fuels,  as  coal,  coke,  wood,  etc.,  may  be  treated  in  a 
similar  manner.  For  hard  coals  the  computation  gives  results 
which  agree  fairly  closely  with  calorimeter  determinations.  As 
the  amount  of  volatile  matter  in  the  coal  increases,  i.e.,  as  the 
hydrocarbons  increase,  there  is  less  certainty  of  fair  agreement, 
although  the  computed  result  is  usually  within  5  per  cent  of  the 
true  value.  The  general  formula  for  a  solid  fuel  may  be  stated 
as  follows: 

Heating  value  = 

14500  C  +  52230  f  H  -  ~~\  +  4000  S  -  1000  H2O  (5) 

L         s  J 
where 

C   =  percentage  of  fixed  and  volatile  carbon. 
H  =  percentage  of  hydrogen. 
O   =  percentage  of  oxygen. 
S   =  percentage  of  sulphur. 

H2O  =  percentage  of  water  in  coal  as  received,  C,  H  and  S 
being  determined  on  the  dry  fuel,  and  then  recomputed  to  the 
basis  of  fuel  as  received. 

The  following  table  shows  the  analyses  of  two  coals  and  the 
heating  values  as  found  by  calorimeter  and  by  above  formula. 
Both  analyses  are  taken  from  Poole's  "The  Calorific  Power  of 
Fuels:" 


136 


INTERNAL  COMBUSTION  ENGINES 


Name 

Kind 

C 

H 

O 

N 

s 

H2O 

Ash 

Heating  Value 
as  received 

By  Cal.  (Computed 

Treverton  .  . 
Carnegie  — 

Anthracite 
Bituminous 

90.66 
77.20 

1.73 
5.10 

.78    .001 
7.22  1.68 

I 

1.42 

.84 
1.45 

6.83 
5.93 

14029 
13842 

13988 
13367 

It  will  be  noted  that  the  agreement  in  the  results  for 
the  hard  coal  is  good,  in  the  case  of  the  soft  coal  the 
computed  result  is  3.5  per  cent  smaller  than  that  determined 
by  calorimeter. 

Attempts  have  been  made  from  time  to  time  to  adapt  formulae 
to  the  approximate  analyses  of  coal,  i.e.,  those  in  which  only 
fixed  carbon,  volatile  matter,  water  and  ash  are  determined.  All 
these  attempts  have  not  given  satisfactory  results  owing  to  the 
varied  composition  of  the  volatile  matter  in  various  coals. 

AIR  REQUIRED  FOR  COMBUSTION  AND  THE  PRODUCTS  OF  COM- 
BUSTION. —  As  already  pointed  out,  the  combustion  of  1  Ib.  of 

2  V  Ifi 
C  to  CO2  requires  -  ^~^  2.66  Ib.  O,  and  that  of  1  Ib.  of  H  to 


H2O    requires 


12 

.5  X  16 
1.0 


=  8  Ib.  O.     Since    air    contains    in    each 


pound  only  .23  Ib.  of  oxygen,  the  air  required  for  the  two  cases 
will 


.23 


11.57  Ib.  and  -       =  34.78  Ib.  respectively. 
.23 


The  products  of  combustion  are,  in  the  case  of  carbon,  3.66 
pounds  of  CO2  and,  in  the  case  of  hydrogen,  9  pounds  of 
H2O,  if  the  theoretical  amount  of  oxygen  has  been  used  in 
each  case. 

With  the  aid  of  these  fundamental  figures,  the  air  required 
and  the  resulting  products  of  combustion  may  be  computed  for 
any  given  fuel,  solid,  liquid  or  gaseous,  if  the  composition  of  the 
fuel  is  known; 

In  general,  any  fuel  which  contains  per  pound  say  C  Ib.  car- 
bon, H  Ib.  hydrogen  and  O  Ib.  oxygen,  requires 

2.66  C  +  8  H  -  O 


.23 


pounds  of  air  for  its  complete  combustion. 


In  gas-engine  practice,  however,  the  case  of  gas  fuels  is  of 
much  more  importance,  and  for  this  we  can  derive  the  following 
general  formulae: 


COMBUSTION  137 

(a)    FOR  ONE  POUND  OF  GAS.  —  Let  the  gas  consist  of 
N!  lb.  CO  +  N2  Ib.  H  +  N3  Ib.  CH4  +  N4  Ib.  C2  H4  +N5  Ib.  C2H2 
+  N6  lb.  O  +  N7  lb.  N  +  N8  lb.  CO2  +  N9  lb.  H2O  =  1 
pound. 
Air  theoretically  required  per  pound  of  gas 

^  .57  Nt  +  8  N2  +  3.99  N3  +3.43  N4  +3.07  N5  -  N6  poundg 

(6) 

Products  of  combustion  per  pound  of  gas 

CO2  =  [1.57  N!  +  2.74  N3  +  3.14  N4  +  3.38  N5  +  NJ  pounds    (7) 
and 
H2O  =  [9  N2  +  2.25  N3  +  1.29  N4  +  .69  N5  +  N9]  pounds        (8) 

Besides  the  above  amounts  of  CO2  and  H2O,  the  products  of  com- 
bustion will  also  contain  any  excess  oxygen  that  may  have  been 
used  together  with  the  nitrogen  brought  in  by  the  oxygen. 

If  the  analysis  of  the  exhaust  gas  shows  free  oxygen,  the  excess 
coefficient  for  the  air  used,  provided  the  fuel  gas  itself  carries 
no  nitrogen,  may  be  computed  from  the  formula 

N 


U  = 


N  -  3.76  O 


where  N  =  per  cent  of  nitrogen,  O  =  per  cent  of  free  oxygen 
in  the  exhaust  gas,  by  volume  and  3.76  is  the  volume  ratio  of 
N  to  O  in  air.  This  formula,  together  with  the  two  given  above 
for  CO2  and  H2O,  allow  of  a  complete  determination  of  the  pro- 
ducts of  combustion. 

In  case  the  fuel  gas  itself  carries  N,  the  determination  of 
the  exess  coefficient  for  the  air  used  is  not  so  simple  and  should 
be  made  according  to  the  method  outlined  on  p.  144. 

(6)  FOR  ONE  CUBIC  FOOT  OF  GAS.  --  Assume  that  the  gas 
has  the  following  analysis: 

Nj  per  cent  by  volume  of  CO 
N2  per  cent  by  volume  of  H2 
N3  per  cent  by  volume  of  CH4 
N4  per  cent  by  volume  of  C2H4 
N5  per  cent  by  volume  of  C2H3 


138  INTERNAL  COMBUSTION  ENGINES 

N6  per  cent  by  volume  of  O2 
N7  per  cent  by  volume  of  N2 
N8  per  cent  by  volume  of  CO2 
N9  per  cent  by  volume  of  H2O 

Air  required  per  cubic  foot,  theoretically, 

Nl  ^  NZ  +  2  N3  +  3  N4  +  2.5  N5  -  N6 

21  -  cubic  feet  (9) 

Products  of  combustion  per  cubic  foot  of  gas 

C02  -  p^  +  N3  +  2N4  +  2N5  +  NJ  cubic  feet  (10) 

H2O  =  [N2  +  2N3  +  2N4  +  N5  +  NJ  cubic  feet  (11) 

Besides  these  amounts  of  CO2  and  H2O  there  will  in  most 
cases  be  additional  amounts  of  free  oxygen  and  of  nitrogen.  The 
volumes  of  these  can  be  determined  from  the  exhaust  gas  analysis 
as  before. 

The  table,  page  139,  gives  the  main  constants  for  the  principal 
gases  met  in  gas  engine  practice. 

The  constant,  R,  can  be  computed  from 


where, 

J=  the  mechanical  equivalent  of  heat  =  778 
and 

m  =  molecular  weight  of  the  gas. 

SAMPLE  COMPUTATION.  —  Given  the  following  chemical  analy- 
sis of  a  producer  gas,  p.  140,  to  determine  its  heating  value,  its 

C* 
molecular  weight  m,  Cp  and  Cv1  R  and-^p.     Also  these  quantities 

C^ 

for  various  mixtures  of  this  gas  with  air,  and  the  amount  of  and 
the  constants  for  the  burned  gases  after  combustion  of  these  fuel 
mixtures. 


COMBUSTION 


139 


Constant 
R 

~CS                 y 

I      S> 

.2 

CO? 

S" 

SiOCOCO           COOi>OOOrH 
l<N(NrH              C^1>-I>-»OO 

3l>iOOi           lOOiCOiOtO 

* 
fa 

0 

rH    t- 

;llgiSslss 

w§ 

0    ° 

(N 

£a 

ft 

CO 

* 

1? 

^   CO    Tt^    CO    ^    ^^   t^w   IN- 

CO 

3 

§* 

1        §1 

3 

Oi 

<N     rH               rH 

1 

PH 

|      £_g 

1  £ 

T- 

5     t^     rH     CO     rH 

H    (N    CO    CO    CO 

I 

8      S 

o  o 

0    CO    00   Oi    CO 
3    tO    tO    Oi    00 

q     Oi     TjH     rH     00 
TH     rH     (N 

00 

^ 

< 
1° 

51 

00    0 

^c 

0    O    to    to    >O 
"^    CO    Oi    CO    Oi 

•}    !>•    rt*    CO    rt< 

rH     rH     rH     rH 

o 

fi 

^ 

8^ 

00 

-  Oi  co  i^  co 

7)    Oi    "*    O    •* 
CO    CO    CO    CO 

:d 

o 

1 

2-        ~ 

^11 

to  c 
to  o 

81 

^     CO     CO     CO     TH     CO     CO     CO     CO     rH 

E 

rH 

* 

| 

1s- 

3 
0 

l>    C 

^0 

^    <N    Tfi    Oi    O 

t<    to    CO    Oi    ^ 
0    Oi    to    -<ti    O 

rH     rH     CO 

||k 

>_] 

t-1 

%t 

CM    0 

5    tO    CO    CO   <N 

0    00    CM    1>    TH 

a"E 

^§§§•§^0    §8 

( 
n 

3       

<     •          £> 

( 

3                          :  ^  12 

5                                                        OX 

• 

5                                  p^  3 

Hydrogen 
n«_i  TIT 

iiliii!«1 

liilillill 

140 


INTERNAL  COMBUSTION  ENGINES 


2»SS 
•s£°  § 


i!. 


TH     T-H     00    rH 
O5    *-l     CO     O 


00     0 


8  8  % 


CO    CO  CO  OO  •'t'  O    00 

TP    Oi  Oi  CO  "^  Oi    OO 

CO    O  O  CD  t^  O    00 

r^  co  '  <N 


CO        _;  M 

oo      Hi's 


S 


CO    1C    CO    CO    O5 
CO    (N    (N    (M    (N    t^ 


IO   lO   !>• 
t--   iO   Oi 


CO      T^      T^      t^ 

Oi       O       ^       ^^ 

10    Tt    <N    (M 


CO 


Tt^  00  CO  CO  CO 

"7    !>.  CO  CO  !>•  »O 

^     r-t  Tt<  CO  i-H  i-l 

(N 


S3 


t^  ^^ 
CO  00 
Ol  CO 


^D  CO  ^^  CO  C^ 

GO  -^  00  00  O 

f>»  -^H  |^»  j^»  oo 

o  o  o  o  o 


CO    OO 

O     CO 

O    «O 


co  i>  I-H  I-H  oo 

GO    *O    C^    ^^    00 
I-H    (N    O    O    Tt< 


CD 

CO 


CO 


GO 
CTj 
<?\ 


GO 


-  H 

co  ^ 

CO  ^ 

O  Oi 


wj  _^ 

10    "     §  CM 

t^*    5s  o 

Bft   *O  bJD 

gO     ^  « 

CO    X     03  QJ 

-i*  ? 


COMBUSTION 


141 


According  to  equation  (9),  the  theoretical  amount  of  air  re- 
quired by  this  gas  per  cubic  foot 

9^07  _J_    187*3 

+  (2  X  .0031)  +  (3  X  .0031)  -  .0003 


.21 


.2342 
.21 


=  1.12  cubic  feet. 


The  following  table  gives  in  the  first  column  the  constants  for 
the  theoretical  air-gas  mixture.  The  second  and  third  columns 
assume  that  an  excess  of  air  is  used,  in  the  first  case  equal  to 
1.5-1. 12  =  .38  cubic  feet,  in  the  last  case  equal  to  2.0-1. 12  =  .88 
cubic  feet: 


CONSTANTS  FOR  VARIOUS  MIXTURES  OF  ABOVE  DOWSON  GAS 
WITH  AIR 


Ratio  air  to  gas: 
By  volume,  V     = 

1    19 

I       C 

By  weight,   W    =  

1      QC 

1    7Q 

2   3Q 

Weight  of  standard  cu  ft.  of 

mixture   In^j     — 

Heating  value  of  standard  cu.  ft.  of  mixture, 
B.T.U.       146'9 

.0744 

.0753 

.0772 

l  +  V  ' 
D     64  +  53.7  W 

69.4 

KO     0 

58.8 
K7   a 

49.0 

Kft     Q 

W+l 
.2887  +  .238  W 

.2595 

.2560 

.2529 

p             W+  I 
n       .2064+.  169  W 

1849 

1824 

1800 

W+l 

Cp 

cv 

1.403 

1.404 

1.405 

The  next  table  gives  the  corresponding  constants  for  the 
burned  gases  resulting  from  the  combustion  of  the  fuel  mixtures 
assumed  above. 

The  changes  occurring  during  combustion  cause  a  change  in 

C1 
the  values  of  R,  C     Cv,  ^  etc.     For  the  theoretical  case,  i.e., 

Cv 

with  1.12  cubic  feet  of  air  to  1  cubic  foot  of  gas,  the  products  of 
combustion  will  be  according  to  equations  (10)  and  (11). 


142 


INTERNAL  COMBUSTION  ENGINES 


CO2  =  (.2507  +  .0031  +  .0062  +  .0657)  =  .3257  cubic  feet. 
H20  =  (.1873  +  .0062  +  .0062)  =  .1997  cubic  feet. 
Since  1.12  cubic  feet  of  air  were  used,  there  must  also  neces- 
sarily be  nitrogen  to  the  volume  of 

[(1.12  X  .79)  +  .4898]  =  1.3746  cubic  feet, 

.4898  cubic  feet  being  due  to  the  nitrogen  in  the  fuel  gas 
itself. 

The  volumes  of  the  exhaust  gases  in  the  second  column  of  the 
table  are  found  as  follows.  The  volumes  of  CO2  and  of  H2O 
are  of  course  the  same  as  before,  since  1  cubic  foot  of  gas  is 
burned  in  every  case.  But  since  only  1.12  cubic  feet  of  air  are 
required  and  1.5  cubic  feet  have  been  used,  the  excess  air  is 
1.5  -  1.12  =  .38  cubic  feet.  This  consists  of  .38  X  .79  =  .3002 
cubic  feet  of  N  and  .0798  of  O.  Hence  the  excess  O  appearing 
will  be  .0798  cubic  feet,  while  the  N  now  is  1.3746  +  .3002 
=  1.6748  cubic  feet. 

CONSTANTS  FOR  THE  BURNED  GASES 


Ratic 
Vol.  < 

Vol.i 
( 
Vol.  < 
Co 
Ra 

%co 

a 

0 

T3 

el 
£1 

Is  o 
.SO 

I 

air  to  fijas  by  vol                         

1.12 
.3257 
.1997 
.0000 
1  .  3746 

1.9000 

2.12 
.896 

10.4 
52.1 

.2478 
.1809 

1.369 

1.5 
.3257 
.1997 
.0798 
1.6748 

2.2800 

2.50 
.912 

8.8 
52.5 

.2462 

.1787 

1.379 

2.0 
.3257 
.1997 
.1848 
2.0698 

2.7800 

3.00 
.926 

7.4 
52.7 

.2446 
.1769 

1.383- 

)f  6xhaust  cases  cu  ft  *  COa           .•••••  

H2O                 

o      

N                

}f  exhaust  gases  to  1  cu.  ft.  of  Dowson  gas, 

•U     ft                                                                                            T^2 

}f  mixture  before 
mbustion                                       *  \ 

tio                             Vz 

vl 

Re-RV* 

Vi 
Ci>  ^ 

^p  1  • 

>     per  pound 
Cv  )               

CP 

Cv" 

COMBUSTION 


143 


The  values  of  Cp  and  Cv  in  the  foregoing  table  are  found  as 
follows.     Consider  the  mixture  with  ratio  =  1.5: 


Burned  Gas 

By  Volume 

By  Weight 

CO2  
H2O    

o  

.3257 
.1997 
0798 

.0399 
.0100 
0071 

N 

1  6748 

1311 

2.2800cu.  ft. 

.  1881  pounds 

For  CO2    Cp  =  .0399  X  .20 


H20 
O 

N 


Cp  =  .0100  X  .48 


=  .0080 
-  .0048 


Cp  =  .0071  X  .217  -  -0015 
Cp=  .1311  X  .244  =  .0320 
For       .1881  Ibs.  2Cp  =  1)463 
.0463 


CP= 


Since  Cp  -  Cv  = 


R 


T1881 


=  .2462 


Cv=  .2462  - 

=  .1787 
and  ^  =  1.379 


778 


Attention  should  be  called  to  the  fact  that  although  consider- 
able contraction  of  volume  occurs,  in  the  case  of  this  gas,  during 
combustion,  still  the  values  of  R,  Cp  and  Cv  are  not  greatly  dif- 
ferent from  the  corresponding  values  before  combustion.  In 
some  other  gases,  as  illuminating  gas  for  instance,  the  change  is 
even  less.  So  that  in  most  ordinary  cases  it  is  sufficiently  accurate 
to  assume  that  these  gas  constants  are  the 'same  before  and  after 
combustion.  Only  in  cases  where  extreme  accuracy  is  desired 
is  this  assumption  not  permissible. 

3.  Computation  of  the  amount  of  air  used  in  excess  of 
theoretical  requirements  from  the  exhaust  gas  analysis. 

In  actual  practice  the  exhaust  gases  are  analyzed  for  C02,  O, 
and  N.'  By  the  ordinary  method  of  collecting  these  gases,  the 
water  vapor  originally  present  is -thrown  down  and  does  not  appear 
in  the  analysis.  As  mentioned  before,  if  the  fuel  gas  itself  carries 


144  INTERNAL  COMBUSTION  ENGINES 

no  nitrogen,  the  excess  coefficient  for  the  air  actually  used  may 
be  computed  from  the  formula  given  on  page  137. 

To  show  an  example  of  the  method  of  computation  when  the 
fuel  gas  carries  N,  we  will  take  the  case  of  the  Dowson  gas  above 
given,  and  assume  that  the  exhaust  gas  analysis  gives  the  following 
results:  CO2  -  14.36%,  O  -  5.31%,  and  N  -  80.33%  by  volume. 
We  proceed  as  follows: 

Products  of  Combustion  for  theoretical  ratio  per  cubic  foot 
of  gas,  are: 

CO2    .3257  cu.  ft. 
H2O    .1997     " 
O    .0000     " 

N    .4898     "     due  to  gas  itself  1 

XT  ,     =  1-3746  cu.  ft.  of  N, 

N    .8848     "     due  to  air  used  j 

.   [35.63%  is  due  to  gas. 
of  which  {  _    0__  .     , 

[  64.37%  is  due  to  air. 

Total  1.9000  cu.  ft. 

On  the  basis  of  the  above  exhaust  gas  analysis,  we  now  have: 

Total  N 80.33 

Of  this  amount,  N  due  to  excess  air  will  be  3.76  X  5.31 .  .  =  19.96 
Leaves  N  due  to  the  gas  itself  and  to  air  actually  burned  =60.37 
Of  this  remainder,  as  above  shown,  35.63%  is  due  to  the 

fuel  gas =21.49 

Leaves  N  due  to  the  air  actually  burned =38.88 

Hence  the  excess  coefficient 

38.88  +  19.96  =  58.84  = 
~38^8~      ~  3^88  " 

and  the  real  ratio  of  air  to  gas  for  the  original  fuel  mixture  was 
1.5  X  1.12  =  1.68. 

4.  Calorific  Intensity.  --By  calorific  intensity  is  meant  the 
temperature  that  can  be  realized  theoretically  when  a  unit  weight 
of  any  fuel  is  completely  burned  under  stated  conditions  of  oxy- 
gen or  air  supply.  If  H  represents  the  heating  value  of  the  fuel 
in  B.  T.  TL,  A,  B,  C,  etc.,  the  weights  of  the  various  resulting 
products  of  combustion,  and  CpA,  CpB,  Cpc,  etc.,  the  specific 
heat  at  constant  pressure  of  these  products,  the  general  state- 
ment for  calorific  intensity,  supposing  the  pressure  to  remain 
constant,  is 


COMBUSTION  145 

TT 

Theoretical  Temperature  Rise  =  -j-^  -  —^  -  -=-=  -  °F. 

-f  CCc  + 


Thus  the  calorific  intensity  of  hydrogen  with  theoretical  air 
would  be,  the  products  of  combustion  being  water  vapor  and 
nitrogen, 

52230 

[9  X  .48]  +  126.8  X  .244] 

That  of  C  to  CO2  with  theoretical  air  would  similarly  be 

14500 


[3.66  X.  20]  +  [8.91  X  .244] 

Such  high  temperatures,  however,  are  practically  never  realized, 
due  probably  to  two  causes.  On  the  one  hand  it  is  claimed  that 
the  specific  heat  of  gases  is  not  constant  at  all  temperatures,  but 
that  it  rises  with  the  temperatures;  on  the  other,  dissociation  is 
supposed  to  set  in  before  such  temperatures  are  reached.  These 
matters  will  be  taken  up  somewhat  more  in  detail  in  a  later 
chapter. 


CHAPTER  VII 

GAS-ENGINE  FUELS;  THE  SOLID  FUELS;  GAS  PRODUCERS 

THE  general  requirement  for  a  gas-engine  fuel  is  that  it  must 
mix  readily  with  air  to  form  a  combustible  gas  or  vapor.  Further, 
it  should  burn  with  little  or  no  residue.  This  latter  requirement 
is  not  met  by  the  solid  fuels,  as  coal  dust  for  instance,  and  while 
isolated  attempts  at  using  powdered  coal  directly  have  been 
made,  they  have  so  far  not  been  successful,  owing  to  the  fact 
that  the  resulting  ash  soon  seriously  interferes  with  operation. 

The  gas-engine  fuels  may  be  classed  under  three  heads: 

1.  The  solid  fuels. 

2.  The  liquid  fuels. 

3.  The  gas  fuels. 

It  is  the  rule  that  the  working  medium  in  all  internal  com- 
bustion engines  is  either  a  combustible  gas  or  a  combustible 
vapor,  no  matter  what  the  fuel  may  have  been  from  which  it  was 
derived.  This  implies  gasification  of  the  solid,  and  vaporization 
of  the  liquid,  fuels. 

As  already  pointed  out  above,  the  solid  fuels  cannot  be  em- 
ployed in  their  natural  state.  From  coal  we  derive  by  distillation 
illuminating  gas,  and  from  coal  and  sometimes  other  materials, 
as  wood,  refuse,  etc.,  by  gasification,  the  various  classes  of  pro- 
ducer or  power  gas. 

Illuminating  gas  will  be  further  considered  under  the  head  of 
gas  fuels. 

i.  The  Conversion  of  the  Solid  Fuels  to  Gas:  Producer  Gases. 

-  Gasification  of  solid  fuel  differs  from  distillation  in  the  fact 

that  the  process  is   carried  one  step  further,  i.e.,  not  only  are 

the   gases,  if    any,  driven  off    from    the   fuel,  but    the   carbon 

itself  is  gasified,  leaving  behind  nothing  but  ash. 

The  fundamental  principle  of  all  producer-gas  processes  is 

146 


GAS-ENGINE  FUELS  147 

therefore,  first,  dry  distillation  of  the  fuel,  and,  second,  the  con- 
version of  the  solid  carbon  into  a  combustible  gas,  which  can  only 
be  carbon  monoxide.  If  the  producer  gas  is  found  to  contain 
other  gases  than  those  mentioned,  it  can  only  be  due  to  changes 
in  the  process,  unavoidable  or  otherwise. 

Producer  practice  may  be  carried  on  in  the  following  ways: 

1.  No  steam  or  water  introduced  with  the  air,  resulting  in 
air  gas. 

2.  Producer  blown  up  with  air  for  one  period,  then  blown 
with  steam  alone.     Product  during  first  stage  is  air  gas,  during 
the  second,  water  gas. 

3.  Producer  furnished  with  air  carrying  a  certain  quantity 
of  water  vapor.     Product  is  ordinary  producer  gas,  Dowson  gas, 
etc. 

The  first  of  these  is  seldom  employed  on  account  of  limita- 
tions pointed  out  below.  The  second  and  third  introduce  modi- 
fications into  the  simple  air-gas  process  owing  to  the  presence  of 
water  or  steam. 

AIR  GAS.  —  Considering  the  case  of  the  gasification  of  carbon 
alone,  resulting  in  the  production  of  the  so-called  air  gas,  assume 
the  combustion  of  C  to  CO  complete;  we  then  have 

1  Ib.  of  C  +  1.33  Ib.  O  =  2.33  Ib.  CO  . 

If  C  had  been  burned  completely  to  C02,  the  calorific  power 
would  have  been  14647  B.  T.  U.;  burning  only  to  CO,  however,  we 
obtain  only  4429  B.  T.  U.,  so  that  the  remainder  or  10218  B.  T.  U. 
is  carried  out  of  the  producer  by  the  gas.  made,  and  thus  repre- 
sents its  heat  energy.  4429  B.  T.  U.  appears  as  sensible  heat  in 
the  gas,  and  if  the  gas  is  cooled  before  entering  the  engine  cylinder, 
as  it  usually  is  for  good  reasons,  the  greatest  possible  efficiency 
which  can  be  realized  from  the  gasification  of  1  pound  of  carbon 

10218 
in  this  way  is      "      =  69.6  per  cent.     It  will  be  shown  below  that 

this  is  by  no  means  the  maximum  possible  producer  efficiency. 

WATER  GAS.  —  When  water  vapor  is  led  through  or  over 
incandescent  carbon  the  following  reactions  take  place: 


I.    C2  +  4  H2O  =  2  CO2  +  4  H2. 
II.   C2  +  2  H2O  =  2  CO   +  2  H2. 


148  INTERNAL  COMBUSTION   ENGINES 

I  occurs  at  temperatures  less  than  1250  degrees  Fahrenheit, 
while  II  alone  occurs  at  temperatures  exceeding  1800  degrees 
Fahrenheit;  both  may  occur  between  these  temperature  limits, 
but  the  higher  the  temperature  the  greater  the  formation  of  CO. 
The  maximum  amount  of  CO  is  of  course  the  end  in  view,  and 
assuming  that  no  CO2  is  formed,  i.e.,  temperature  at  or  above 
1800  degrees  Fahrenheit,  we  have  the  following  quantitative 
statement : 

1  Ib.  C  +  1.5  lb.  H2O  =  2.33  Ib.  CO  +  .17  Ib.  H2 
from  which  1  pound  of  water  gas  must  contain 
2.33 


2.33  f  .17 
and 

.17 


=  .932  lb.  Carbon  monoxide 


=  .068  lb.  Hydrogen 


2.33  +  .17 

The  gasification  of  1  pound  of  carbon,  therefore,  in  the  pres- 
ence of  water  vapor  results  in  products  which,  on  complete  com- 
bustion, develop  the  following  amount  of  heat: 

2.33  Ibs.  CO  X  4380      =  10205  B.  T.  U. 

.17  Ibs.  H2  X  62100  =  10557  B.  T.  U. 

Total,       20762  B.  T.  U. 

Heating  value  of  C  to  CO2,  14647  B.  T.  U. 

Excess,  6115B.T.  U. 

The  excess  of  6115  B.  T.  U.  can  only  be  due  to  heat  rendered 
latent  during  the  process.  Water  vapor  on  coming  in  contact 
with  incandescent  carbon  dissociates  into  H2  and  O.  The  latter 
unites  with  C  to  form  CO2,  but  as  the  temperature  of  the  producer 
is  at  or  over  1800  degrees  Fahrenheit,  CO2  is  dissociated  to  CO. 
The  heat  thus  rendered  latent  accounts  for  the  excess  above  shown. 
Now  it  is  evident  that  this  heat  can  only  come  from  the  stock  of 
heat  present  in  the  producer  when  the  blowing  with  steam  first 
starts.  Hence  there  must  be  a  continual  cooling  of  the  producer 
contents  during  the  period  of  water-gas  making.  This  results 
finally  in  a  serious  production  of  CO2  according  to  reaction  I, 
when  the  steam  must  be  shut  off  and  the  contents  of  the 
producer  brought  back  to  incandescence  by  blowing  with  air. 


GAS-ENGINE  FUELS  149 

The  most  unfavorable  operation  of  the  producer  occurs  when  the 
reactions  are  according  to  equation  I.     Under  this  condition 

1  Ib.  C  +  3  Ib.  H2O  =  3.66  CO2  +  .34  H2 
so  that  1  pound  of  water  gas  then  contains 
366 


3.66  +  .34 
and 

.34 
3.66  +  .34 


=  .915  Ib.  CO, 


=  .085  Ib.  Hydrogen 


The  production  of  water  gas  reckoned  on  the  basis  of  coal  or 
carbon  is  not  at  all  efficient,  since  the  heat  in  the  poor  gas  made 
during  the  blowing-up  period  is  very  often  wasted,  and  only  in 
rare  instances  of  utility.  Other  losses  are,  of  course,  those 
through  incomplete  combustion,  radiation,  etc.;  but  these  are 
inherent  in  all  producers  to  a  greater  or  lesser  extent. 

PRODUCER  GAS.  —  Midway  between  air  gas  and  water  gas  we 
find  the  great  class  of  power  gases  for  the  production  of  which 
the  producer  is  blown  continuously  with  a  mixture  of  air  and 
water  vapor. 

To  get  a  fair  insight  into  the  working  of  a  power  gas  pro- 
ducer and  of  the  efficiencies  that  may  be  realized,  we  will  assume 
the  following  definitions  and  quantities.* 

1.  The  heat  supplied  to  a  producer  consists  of  the  heat  fur- 
nished  to   it  in  the  fuel  plus  the  heat  contained  in  steam  and 
air  above  a  certain  fixed  temperature,  say  32  degrees  Fahrenheit. 

2.  The  heat  leaving  the  producer  in  the  gas  is  made  up  of 
the  latent  heat  of  the  gas  plus  the  sensible  heat.     What  the 
quantity  of  heat  considered  as  the  useful  effect  in  efficiency  should 
be  depends  upon  circumstances.     In  furnace  work,  where  it  may 
be  of  advantage  to  employ  the  hot  gas,  the  useful  effect  would  be 
the  sum  of  the  latent  and  sensible  heats  of  the  gas.     In  gas-en- 
gine practice,  on  the  contrary,  the  opposite  is  the  case,  and  the 
useful  effect  would  be  the  latent  heat  only.     In  the  first  case  we 
speak   of   the   hot-gas   efficiency,   in   the   second  of  the  cold-gas 
efficiency. 

*  Adapted  from  the  discussion  of  E.  Meyer,  Zeitschrift  des  Yereins 
deutscher  Ingenieure,  1895,  p.  1523. 


150  INTERNAL  COMBUSTION  ENGINES 

3.  Inside  of  the  producer  the  following  reactions  take  place, 
some  endothermic,  others  exothermic. 

Of  every  pound  of  carbon  the  larger  part  burns  to  CO,  the 
remainder  to  CO2.  The  heat  generated  from  these  two  combus- 
tions is  utilized  in  the  following  ways:  Part  of  it  dissociates  the 
steam  present,  forming  H,  and  CO  or  CO2,  or  both.  How  this 
action  varies  with  the  temperature  of  the  producer  has  al- 
ready been  pointed  out.  A  second  part  of  the  heat  serves  to 
bring  the  fresh  fuel  up  to  the  temperature  of  the  producer,  a 
third  is  lost  by  radiation  from  the  exterior  producer  walls,  and 
the  remainder  appears  as  sensible  heat  in  the  gas  made. 

The  formulae  to  be  derived  will  be  based  upon  one  pound  of  C 
rather  than  upon  one  pound  of  coal,  for  the  reason  that  coals  vary 
greatly  in  composition,  and  it  is  in  every  case  quite  easy  to  change 
from  this  basis  to  that  of  coal  if  the  qualities  of  the  coal  be  known. 
Let 

14500  B.  T.  U.  =  heat  of  combustion  of  1  Ib.  of  C  to  3.66  Ib.  CO2. 

4400  B.  T.  U.  =  heat  of  combustion  of  1  Ib.       C  to  2.33  Ibs.  CO. 

10100  B.  T.  U.  =  heat  of  combustion  of  2.33  Ib.  CO  to  3.66  Ib.  CO2 

£*()  1  C\C\ 

6900  B.  T.  U.  =  -       -  =  heat   required  to   dissociate   1   Ib.   of 
9 

water  vapor  under  producer  conditions. 

x   =  part  of  1  Ib.  of  C  burning  to  CO2. 

(1  —  x)  =  part  of  1  Ib.  of  C  burning  to  CO. 

y  =  pounds  of  steam  introduced  per  Ib.  of  C. 

A  =  heat  furnished  in  steam. 

B  =  heat  furnished  in  air. 

C  =  heat  required  to  bring  fresh  fuel  to  temperature  of 
producer. 

R  =  heat  lost  by  radiation. 

S  =  sensible  heat  of  the  gas. 

All  of  the  above  heat  quantities  are  per  pound  of  carbon  gasi- 
fied, and  above  a  temperature  of  say  32  degrees  Fahrenheit. 

With  this  notation  the  general  heat  equation  for  the  producer 
may  be  stated  as  follows,  based  on  1  Ib.  of  carbon: 

4400  (1  -  x)  +  14500  x  +  A  +  B  =  6900  y  +  S  +  R  +  C 

The  heat  that  will  be  generated  by  the  combustion  of  the  volume 
of  gas  formed  comes  from  CO  and  H. 


GAS-ENGINE  FUELS  151 

Heat  generated  in  gas  per  pound  of  C  gasified 

=  [10100  (1  -  x)  +  6900  y.]  B.  T.  U. 

6900  y  for  the  heat  generated  by  H  is  obtained  by  considering 
that  we  must  receive  as  much  heat  from  the  combustion  of  the  H 
in  the  gas  as  was  rendered  latent  during  dissociation  of  the  amount 
of  H2O  required  to  furnish  it. 

Heat  supplied  per  pound  of  C  gasified  =  14500  +  A  +  B. 
Hence 

10100  (1  -  x)  +  6900  y 
Cold-gas  efficiency  145QO  +  A  +  B 

10100  (1  -  x)  +  6900  y  +  S 
Hot-gas  efficacy  14500  +  A  +  B 

In  the  latter  case,  no  part  of  the  sensible  heat  of  the  gas  is 
abstracted  before  the  gas  is  used.  In  practice  there  is  always 
some  loss  of  temperature  between  the  producer  and  the  place 
where  the  gas  is  used,  hence  S  is  never  fully  obtained. 

If  in  the  above  general  heat  equation  the  values  of  x,  A,  B,  C, 
R  and  S  are  known,  the  value  of  y,  i.e.,  the  pounds  of  steam  to  be 
used  per  pound  of  carbon,  may  be  computed.  The  composition 
of  the  resulting  producer  gas  may  be  computed  as  follows,  using 
the  above  notation: 

COMPOSITION  BY  WEIGHT  PER  POUND  OF  CARBON  GASIFIED. 

CO    =  (1  -  x)  ~=  2.33  (1  -  x)  pounds 

C02  =~x  =  3.66  x  pounds 

H   =  —y  =  --  pounds 

The  amount  of  N  is  found  as  follows: 

i  (\ 
Oxygen  required  for  CO  =  (1  -  x)  -^     =  1.33  (1  —  re)  pounds 

32 

Oxygen  required  for  C02  =  y~  x  =  2-66  x  pounds 

Oxygen  produced  by  dissociation  of  H2O. 

16          8 

=  182/=92/P°UndS 
.  • .  O  required  from  air  blast 


152  INTERNAL  COMBUSTION  ENGINES 

=  1.33  (1  -  x)  +  2.66  x  -  |  y  pounds 

=  1.33  (1  +  x)  —  -  y  pounds 
y 

[8     ~1    100 
1.33  (1  +  x  )  —  -  y     ^-  pounds 
9     J  26.5 

Hence  also  N  brought  in  by  air  blast  is 

o     ~|  76  'i 
1.33(1  +  x)  -^y    ^| pounds 

The  total  weight  of  gas  produced  by  one  pound  of  carbon 
therefore  is 

=  2.33  (1  -  x)  +  3.66  x  +  |  + 1~  1.33  (1  +  x)  -  ^y  1^|  pounds 

L  J 

=  (6.67  +  5.67  x  —  2.77  y)  pounds  of  producer  gas. 

COMPOSITION  BY  VOLUME  PER  POUND  OF  CARBON  GASIFIED. 

Volumes  at  32  degrees  and  14.7  Ib.  pressure. 

Weight  per  cubic  foot  of  the  various  gas  under  standard  con- 
ditions. 

CO  =  .07807  Ib.,  CO2  =  .12267  Ib.,  H  =  .00559,  N  =  .07831. 

Hence,   from    the   above  weight    computations,    we  may   write 

directly. 

o  0.0.  r 

Volume  of  CO  =    '***  (1  -  x)  =  29.84  (1  -  x)  cu,  ft. 
.07oU7 


3.66 
.12267 


Volume  of  CO2  =  ^^x  =  29.02  x  cu.  ft. 


Volume  of  H  =  _.  L~^=  19.87  y  cu.  ft. 

76.5 


[ 


J3.5X. 07831 
=  (55.51  +  41.74  x  -  37.10  y)  cubic  feet, 

From  this 

Total  volume  of  gas  per  pound  of  C  gasified 

=  [29.84(1  -x)  +  29.02  x  +  19.87  y  +  55.51  +  41.74  x  -  37.10 

cubic  feet. 
=  (85.35  +  40.92  x  -  17.23  y)  cubic  feet. 


GAS-ENGINE  FUELS  153 

2.  Theoretical  Yield  of  Producer.  —  If  it  is  supposed  that 
no  CO2  is  formed,  that  all  the  sensible  heat  produced  in  the 
generator  is  recovered  in  making  steam  and  preheating  air  and 
fresh  fuel,  and  that  no  radiation  has  taken  place,  we  shall  have 

x  and  R  =  0,  and  S  =  A  +  B. 

Under  these  theoretical  conditions,  the  general  heat  equation 
(p.  151)  then  becomes 

4400  =  6900  y  +  C. 

The  value  of  C  is  approximately  .2  X  1800  =  360  B.  T.  U. 
Hence 

4140  -  6900  y, 

4140 
from  which  y  =  7^.^.  =  -600  pounds  of  steam   per  pound  of  C 


gasified.  ^ 

The  theoretical  yield  of  gas  per  pound  of  carbon  under  these 
conditions  will  be 

29.84  cubic  feet  of  CO. 

19.87  X  .600  =  11.92  cubic  feet  of  H 
and 

55.51  -  37.10  X  .600  =  33.25  cubic  feet  of  N. 

Total  volume  of  yield  =  75.01  cubic  feet  per  pound  of  C. 
Composition  of  gas,  per  cent  by  volume, 

39.8  per  cent  CO,  15.9  per  cent  H,  44.3  per  cent  N. 

Taking  the  higher  heating  value  of  R  at  346  B.  T.  U.  per 
cubic  foot,  and  the  heating  value  of  CO  at  342  B.  T.  U.  per  cubic 
foot,  the  gas  yield  from  1  pound  of  C  will  develop 

(29.84  X  342)  +  (11.92  X  346)  =  14249  B.  T.  U. 

The  higher  heating  value  per  cubic  foot  of  this  theoretical 
gas  is  therefore 

14940 

4^=*  =  187.2  B.  T.  U.  per  cu.  ft. 
7  o.Ul 

In  actual  practice,  however,  x  and  R  cannot  =  0,  neither 
is  S  =  A  +  B;  i.e.,  not  all  of  the  heat  appearing  as  sensible 
heat  in  the  gas  leaving  the  producer  is  ever  recovered.  To 


154  INTERNAL  COMBUSTION   ENGINES 

make  clear  what  happens  under  these  circumstances,  the  follow- 
ing table  is  constructed.  In  this  table  it  is  assumed  that  the 
heat  furnished  in  steam  and  air  per  pound  of  carbon  equals  1000 
B.  T.  U.  =  (A  +  B)  in  all  cases,  and  that  the  sum  of  the  heat 
losses  due  to  radiation,  R,  and  sensible  heat  of  the  gas,  S,  =  1640 
B.  T.  U.  per  pound  of  carbon. 

The  heat  furnished  the  producer  per  pound  of  C  will  then  in 
all  cases  be  14500  +  1000  =  15500  B.  T.  U.,  while  the  heat 
accounted  for  will  be  15500  -  (1640  +  360)  =  13500  B.  T.  U., 

1 S500 
so  that  the  generator  efficiency  on  hot  gas  in  all  cases  = 

looUU 

=  87.2  per  cent.  It  is  further  assumed  for  illustration  that  only 
the  amount  of  carbon  burned  to  CO2  per  pound  of  carbon  gasi- 
fied varies. 


GAS-ENGINE  FUELS 


155 


o>  .2  o>  3  -^  "2  6  & 

p    *>•    t>.    p    <N 

1>    CO    *O    »O    lO 

i-H      rH      i-H      i-H      i-H 

Composition,  %  by  volume 

» 

IO      O      »O      O      i-l 
00     CO     CO     r-1     oi 

w 

«q   I-H   T^   t^.   oo 

1-1     I-H     1-1    <M     (N 

o 
o 

OS    <N    O5    CO    «3- 
00    TJH    oi    10    I-H 
CO     CO     (N     (N     (N 

o 
o 

o     l^;     (N     |>     co 

M   *>   o   co 

i—  i   i—  i 

Cubic  feet  of  gas  per  pound  of  C 

1 
3 

o   i>   co   O5   rt< 

CO       Tt*       CO      t^.      Qi 

s 

a 
o 

O     O5    O     O     CO 

O     00     C3     i-l     CO 
l>    1>    00    00     00 

- 

(N       Tt<       TfH       1-1       00 

(N     Oi    00    »O    ^j 
l>-    id    rti    CO    (N 

CO     CO     CO     CO     CO 

w 

o   o   >o   o   »o 

OO-    t^-    lO    lO    TP 

O5    (N     ^O    00    i-l 

i-H      i-H      i—  1      C^ 

o 
o 

TJH    10    O    O    O 
00     00    Oi     Oi     O5 
Oi    CO    CO    O    t>> 
<M     <N     (N     (N     I-H 

8 

0    0    0    0    0 
°     O5     00     l>     CO   • 

oi   »d   06   i-l 

Jl* 

CO     Oi     CO     O?     Oi 
Oi     CO     00     CO     t"^ 

1*1  2  S 

o  « 

o   o   o   o   o 
1-1   ca   co   TP 

156  INTERNAL  COMBUSTION   ENGINES 

In  commenting  upon  the  above  table,  Meyer  points  out  that 
as  the  percentage  of  CO2  in  the  gas  increases,  the  heating  value 
of  the  gas  decreases,  but  since  at  the  same  time  the  percentage 
of  H  and  the  volume  of  gas  per  pound  of  C  increase,  it  is  not 
always  right  to  conclude  from  analysis  alone  that  the  efficiency 
of  the  generator  is  less  with  a  fairly  high  than  with  a  low  percent- 
age of  CO2  in  the  gas.  In  general  terms  it  can  be  stated,  how- 
ever, that  the  lower  the  temperature  of  the  generator,  the  greater 
the  formation  of  CO2,  and  the  greater  also  the  loss  of  heat  in 
sensible  heat  of  the  resulting  gas. 

Referring  to  the  gas  engine  itself,  a  high  percentage  of  CO2 
in  the  gas  means  a  low  engine  capacity,  since  this  high  percentage 
is  usually  also  accompanied  by  an  increased  amount  of  the  other 
indifferent  gases. 

3.  Gas  Producers  in  Practice.  —  Turning  now  to  actual  gen- 
erator practice,  we  find  the  following  main  points  of  difference: 
The  fuel  is  not  pure  carbon,  but  some  impure  form  of  it,  as  coal, 
coke,  lignite,  peat,  or  wood.  This  in  itself  merely  results  in  a 
lower  yield  of  gas  per  pound  of  fuel  fired  than  that  above  com- 
puted, and  this  decrease  is  further  emphasized  by  the  fact  that 
some  of  the  unburned  carbon  in  the  fuel  is  always  lost  in  the  ash. 
A  complex  fuel  being  used  containing  gases  which  are  distilled 
off  during  the  first  part  of  the  process,  the  resulting  producer 
gas  will  have  a  somewhat  different  composition  than  that  above 
computed.  The  main  difference  is  due  to  the  addition  of 
hydrocarbons,  and  this  difference  is  therefore  greater  with 
bituminous  coals  than  with  any  of  the  other  fuels.  The  use 
of  any  of  the  above-mentioned  fuels  results  also  in  other 
complications  more  or  less  difficult,  depending  upon  the  fuel 
used.  Such  are  the  formation  of  tar,  dust  carried  by  the  gas, 
etc.,  all  of  which  make  a  cleaning  of  the  gas  imperative  before 
it  can  be  used. 

The  primary  consideration  in  the  operation  of  the  gas  pro- 
ducers is  perhaps  the  kind  of  fuel  used.  The  points  to  be  con- 
sidered in  this  connection  are:  percentage,  of  water  carried  by 
fuel,  amount  and  kind  of  ash,  tar-forming  ingredients  of  the  fuel, 
size  of  fuel,  and  whether  it  cokes  or  not. 

A  high  percentage  of  water  has  a  direct  effect  in  lowering  the 
temperature  of  the  producer,  besides  lowering  the  heating  value 


GAS-ENGINE  FUELS  157 

of  the  gas  per  cubic  foot  as  made.  A  large  amount  of  ash  makes 
more  frequent  cleaning  out  necessary,  or  it  is  likely  to  result  in  a 
partial  stoppage  of  the  air  supply.  If  the  ash  should  be  easily 
fusible  the  case  is  much  more  complicated,  as  this  results  in  bad 
clinkering.  The  size  of  the  fuel  should  be  a  happy  medium. 
Small  fuel,  i.e.,  screenings,  etc.,  clog  up  easily  and  in  any  case 
require  a  higher  blast  pressure.  Large  fuel,  on  the  other  hand, 
offers  too  little  surface  for  gasification  and  is  apt  to  let  much  water 
and  CO2  escape  unreduced.  A  coking  coal  nearly  always  gives 
trouble  from  this  cause,  and  it  necessitates  constant  breaking  up 
of  the  charge. 

The  formation  of  tar,  which  results  especially  when  bitumi- 
nous coals  are  gasified,  makes  a  cleaning  of  the  gas  for  engine  pur- 
poses indispensable.  Tar  results  when  some  of  the  hydrocarbon 
gases  are  condensed  through  cooling  in  the  gas  mains  and  pipes. 
If  these  gases  reach  the  cyclinder  their  combustion  is  likely  to 
result  in  a  strong  deposit  of  soot.  In  either  case  the  operation 
of  the  engine  will  soon  be  seriously  interfered  with.  Tar  can  be 
almost  entirely  removed  from  the  gas  by  washing  it,  but  this 
process  requires  constructions  fully  as  costly  as  the  producer 
itself  and  hence  other  methods  have  been  employed. 

The  tar-forming  gases  are  always  those  which  are  formed 
from  the  dry  distillation  of  the  coal,  hence  most  trouble  is  en- 
countered with  bituminous  coal,  less  with  lignite  and  still  less 
with  anthracite.  For  this  reason  anthracite  and  coke  producers 
have  been  most  successful,  although  producers  using  brown 
coals  and  lignites  are  in  operation,  as  are  also  those  using  bitu- 
minous coal,  but  with  less  success.  This  does  not  apply  to  steel 
works  where  bituminous  coal  is  used  extensively  for  gasification. 
But  there  the  gas  is  used  mostly  hot  and  less  trouble  from  tar  is 
experienced. 

The  tar  gasee  can  be  "fixed,"  i.e.,  changed  to  permanent 
gases  when  the  producer  gas  containing  them  is  led  through  an 
incandescent  bed  of  fuel  before  entering  the  gas  mains.  In  this 
case  the  tarry  hydrocarbons  are  changed  either  to  H2O  and  CO2 
or  split  up  into  CO  and  H.  In  some  producers  only  the  gases 
resulting  from  the  dry  distillation  are  handled  in  this  way.  In 
either  case  the  tarry  hydrocarbons  are  fixed,  and  no  elaborate 
cleaning  apparatus  for  the  gas  is  required.  The  necessity  for 


158  INTERNAL  COMBUSTION  ENGINES 

treating  bituminous  producer  gas  in  this  way  has  resulted  in 
various  constructions  of  producer,  a  few  of  which  are  given 
below. 

Gas  producer  installations  may  be  divided  into  three  classes : 

a.  Pressure     Producers.  —  -  In    these    air     and     steam     are 
furnished  to  the  fuel  bed  by  a  blower  or  fan.     The  ash  pit  of  the 
producer  must   be  enclosed,   making  the  removal  of  ash  com- 
plicated or  the  action  of  the  producer  intermittent,  unless  the 
water-bottom  type  is  used.     Steam  for  blowing  is  usually   fur- 
nished by  a  separate  boiler.     Since  the  rate  of  production  of  gas 
is  usually  not  regulated  according  to  the  demand  for  gas  directly, 
a  gas  holder  is  usually  necessary  for  this  type. 

b.  Suction    Producers.  —  In   this    class   the   air   and    steam 
are  drawn  through  the  producer  by  the  suction  of  the  engine 
cylinder.     The  production  of  gas  is  thus   directly  regulated   by 
the  demand.     The  ash  pit  remains  open,  and  steam  enough  can 
usually  be  generated  by  the  sensible  heat  of  the  gas. 

Suction  gas  producers  have  nearly  replaced  pressure  producers 
for  gas-engine  purposes.  Some  of  the  obvious  advantages,  as 
open  ash  pit,  absence  of  separate  boiler  and  of  gas  holder,  have 
been  pointed  out  above.  The  dangers  at  first  supposed  to  be 
inherent  in  this  system  have  failed  to  materialize.  Leaks  in  a 
pressure  system  may  lead  to  a  poisoning  of  the  atmospheric  air 
by  the  color-  and  odorless  CO,  positively  dangerous  to  attendants. 
Leaks  in  a  suction  system  only  result  in  an  in-leakage  of  air. 
That  this  can  never  happen  to  such  an  extent  as  to  form  an  ex- 
plosive mixture,  except  through  a  combination  of  extraordinary 
circumstances,  is  at  once  evident  when  we  consider  that  the  ratio 
of  air  to  producer  gas  for  such  a  mixture  would  have  to  be  at  least 
1  to  1. 

In  spite  of  such  advantages  the  suction  system  is  by  no 
means  perfect.  The  regulation  of  the  water  supply  to  control 
the  amount  of  H  in  the  gas,  the  vaporizer  for  the  water,  and 
the  cleaning  apparatus  are  still  points  which  admit  of  improve- 
ment even  in  the  most  recent  form. 

c.  Combination   Producers.  —  The    air    and   steam   mixture 
is  drawn  through  the  producer  by  a  fan  and  the  resulting  gas 
forced  by  the  same   fan  to  the  engine.     The  producer  in  this 
system  is  thus  of  the  suction  type. 


GAS-ENGINE  FUELS  159 

PRESSURE  PRODUCERS. — Taylor.  Fig.  7-1  shows  the  Taylor 
producer  made  by  R.  D.  Wood  &  Co.  of  Philadelphia.  In  their 
publications  on  the  producer  this  company 
lays  down  the  following  requirements  for  a 
successful  pressure  producer.  Most  of  these, 
however,  apply  to  producers  in  general. 

1.  A  continuous  and  automatic  feed;    the 
former    for    regularity  and    uniformity  of  gas 
production  with    improved  quality,  the    latter 
for  eliminating  negligence  of  attendants. 

2.  A  deep  fuel  bed  carried  on  a  deep  bed 
of  ashes;    the  first  to  make  good  gas,  and  the 
second  to  prevent  waste  of  fuel. 

3.  Blast    carried    by.  conduit    through   the 
ashes  to  the  incandescent  fuel. 

4.  Visibility  of  the  ashes,  and  accessibility    FIG.  7-1.  —  Taylor 
of  the    apertures   for   their   removal,  arranged  Producer. 

so  that  operator  can  see  what  he  is  doing. 

5.  Level,  grateless  support  for  the  burden,  insuring  uniform 
depth  of  fuel  at  all  points,  and  consequent  uniformity  in  the  pro- 
duction of  gas. 

These  points  are  well  covered  in  the  design  of  the  producer. 
The  fuel  is  admitted  through  a  distributing  hopper  which  keeps 
the  layer  of  fuel  level  over  the  cross-section.  The  bed  of  ashes 
is  kept  at  about  6  inches  over  the  top  of  the  air  pipe,  thus  protect- 
ing it  from  direct  heat.  The  entire  charge  in  the  producer  is 
supported  by  a  plate  whose  diameter  is  somewhat  greater  than 
that  at  the  bosh.  As  necessity  requires,  this  plate  can  be  revolved 
and  the  ashes  are  scraped,  or  they  fall  off,  into  the  closed  ash  pit, 
which  is  under  blast  pressure.  The  grinding  action  ensuing  when 
the  plate  is  revolved  settles  the  contents  of  the  producer  and 
thus  closes  up  any  free  air  channels  that  may  have  been  formed. 
Once  a  day  the  pit  must  be  opened  for  the  removal  of  the  ash. 
Blast  is  supplied  generally  by  a  steam  jet. 

Morgan.  Somewhat  similar  in  design  is  the  Morgan  pro- 
ducer, Fig.  7-2.  The  main  point  of  difference  is  in  the  removal 
of  the  ash.  The  fuel  here  is  also  admitted  through  a -continuous 
automatic  feeding  device.  The  blast  is  controlled  by  a  steam 
injector  so  designed  as  to  maintain  a  proper  proportion  between 


160 


INTERNAL  COMBUSTION  ENGINES 


air  and  steam.     The  make  of  gas  can  be  completely  controlled  by 
the  adjustment  of  a  j-inch  steam  valve. 

This  producer  is  of  the  water- 
bottom  type,  i.e.,  the  ashes  fall  into  a 
water  seal  at  the  bottom,  and  may 
there  be  removed  without  stopping 
the  operation  of  the  producer.  This  is 
not  easily  done  when  a  grate  or  similar 
device  is  used  in  a  pressure  producer. 
For  certain  fuels,  especially  those 
highly  bituminous  or  those  where  ash 
is  apt  to  clinker,  the  water-bottom 
producers  possess  some  advantage  over 
the  others.  About  three  feet  above  the 
water  level  in  the  ash  pan,  and  some 
inches  above  the  top  of  the  blast  dis- 
tributing pipe,  a  number  of  sight 
holes  are  arranged  around  the  circumference  of  the  producer. 
Through  these  the  zone  of  combustion  may  be  watched.  The 
top  of  the  producer  is  covered  with  a  shallow  water  pan.  Poke 
holes  through  the  top  with  water-sealed  covers  are  also  provided. 


FIG.  7-2. —  Morgan 
Producer. 


H    i 


FIG.  7-3.  —  Wile  Producer  Installation. 

Wile.     A  complete  Wile  pressure  gas  plant  is  shown  in  Fig. 

7-3.*     Steam  under  about  40  pounds  pressure  is  generated  in  the 

boiler,  A,  and  enters  the  generator  through  the  injector,  7,  mixed 

with  air.     The  gas  made  passes  through  the  seal  box,  D,  and  the 

*  J.  I.  Wile  in  Power. 


GAS-ENGINE  FUELS 


161 


scrubber  to  the  gas  holder.  This  is  the  ordinary  arrangement, 
but  it  is  open  to  objection  when  the  load  is  extremely  variable. 
In  such  a  case  it  is  usual  to  arrange  the  gas  holder  so  that  it  shuts 
off  steam  at  /  when  the  holder  is  full.  The  contents  of  the  pro- 
ducer then  cool,  and  a  further  cooling  results  when  the  steam  is 
next  turned  on.  The  temperature  ranges  in  the  producer  are 
therefore  apt  to  be  high  under  such  conditions.  To  meet  this 
difficulty  the  design  can  be  changed  by  placing  the  steam  injector 
at  B,  above  the  seal  box  D.  The  gas  holder  is  connected  with  the 
seal  box  by  a  return  pipe  E.  When  the  gas  holder  is  up,  catch  H 
in  the  gas  holder  opens  the  return  valve^and  the  injector  B  merely 
draws  on  the  gas  holder,  placing  the  generator  temporarily  out  of 
commission.  When  the  gas  holder  falls,  the  return  valve  closes, 
the  injector  draws  on  the  generator,  and  gas  is  again  made.  In 
this  design  the  arrangement  at  /  is  then  merely  a  saturator,  and 
the  plant  is  really  a  combination  plant,  the  generator  being  under 
suction. 


FIG.  7-4.  —  Koerting  Pressure  Producer. 

Koerting,  Hannover*  Fig.  7-4  shows  a  Koerting  pressure  plant. 
The  gases  made  during  the  firing-up  period  escape  through  the 
pipe  a.  Should  the  natural  draft  not  be  strong  enough,  it  may 
be  increased  by  means  of  a  small  steam  blower  in  pipe  a.  After 
the  flame  at  the  try  cock  shows  dark  red,  and  not  blue,  the  valve 
b  is  closed,  and  the  gas  made  sent  through  the  pre-heater,  scrub- 
*  Giildner,  Entwerfen  und  Berechnen  der  Verbrennungsmotoren,  p.  384. 


162 


INTERNAL  COMBUSTION   ENGINES 


ber,  and  sawdust  purifier  to  the  gas  holder.  The  make  of  gas  is 
controlled  by  the  gas  holder  through  the  chain  C,  which  acts 
upon  the  blast  through  a  throttle  valve  at  d.  According  to  pub- 
lished figures,  the  average  analysis  of  the  gas  made  is,  by  volume, 

H,  18  per  cent;  CO,  26  per  cent;  CM  H2w,  2  per  cent. 

CO2,  7  per  cent;  N,  47  per  cent;  Efficiency,  80-82  per  cent. 


'///////////////////////^ 

FIG.  7-5.  —  Deutz  Pressure  Producer. 

Deutz*     The  steam  used  for  the  blower  a,  in  the  Deutz  plant, 

Fig.  7-5,  is  superheated  in  a  coiled  pipe  above  the  fuel  in  the  boiler. 


FIG.  7-6.  —  Poetter  Producer. 
*  Giildner,  Entwerfen  und  Berechnen  der  Verbrennungsmotoren,  p.  384. 


GAS-ENGINE  FUELS 


163 


The  air  is  pre-heated  by  the  heat  of  gases  in  the  heater  C.  The 
opening  b  is  used  to  try  the  gas  during  firing  up.  Arrangements 
of  scrubber  and  purifier  are  similar  to  those  already  described. 

Poetter.  The  Poetter  producer,*  Fig.  7-6,  is  especially  de- 
signed for  bituminous  coal.  The  fuel  charged  is  distilled  while 
still  in  the  hopper,  the  gases  formed  are  drawn  off  by  special 
steam  blower  and  are  led  through  the  pipe  Cd  under  the  grate. 
Air  for  blast  is  provided  through  e  /.  The  gas  made  escapes  at  a, 
and  is  first  used  to  raise  the  steam  required  in  a  boiler.  It  is 
then  led  through  cooler,  scrubber,  coke-  and  sawdust  purifier  to 
the  gas  holder.  Schottler,  in  describing  a  plant  of  Poetter  pro- 
ducers at  Johannesburg,  surmises  that  their  operation  might  cause 
trouble,  although  the  kind  of  coal  used  at  Johannesburg  is  not 
stated. 


FIG.  7-7.  —  Mond  Producer  Plant. 

Mond.  When  a  producer  is  blown  with  a  large  excess  of 
steam,  a  great  deal  of  it  will  go  through  undecomposed.  At  the 
same  time,  however,  the  quality  of  the  gas  made  undergoes  some 
radical  changes.  The  quantity  of  H  in  the  gas  will  be  high, 
sometimes  up  to  25  per  cent,  while  on  account  of  the  low  pro- 
ducer temperature,  a  great  deal  more  of  the  C  is  burned  to  CO2 
than  is  ordinarily  the  case.  A  further,  and  important,  change  is 
that  a  great  deal  of  the  N  is  changed  to  ammonia,  a  reaction 
which  does  not  take  place  in  producers  run  under  the  ordinarily 
higher  temperatures.  To  recover  this  ammonia  is  an  important 
consideration.  This  is  the  process  of  Mond. 

A  Mond  gas  plant  consists  essentially  of  two  parts,  the  pro- 
ducer and  the  condensing  and  recovery  plant,  Fig.  7-7. 
*  Rev.  Mec.,  1904,  p.  484. 


164  INTERNAL  COMBUSTION  ENGINES 

The  details  of  the  producer  A  do  not  differ  much  from  those 
already  described.  It  is  of  the  water-bottom  type.  The  gas 
made  passes  through  the  regenerators  B.  These  consist  of  double 
wrought-iron  tubes  united  alternately  top  and  bottom.  The  hot 
gases  pass  through  the  inner  tubes,  heating  the  mixture  of  steam 
and  air,  used  for  blowing  the  producer,  which  flows  through  the 
outer  tubes  in  the  opposite  direction.  The  gas  next  passes 
through  the  washer  C.  This  is  a  large  chamber  partly  filled  with 
water.  By  means  of  dashers,  driven  by  D,  the  chamber  is  kept 
filled  with  water  spray.  The  gas  is  cooled  considerably  in  pass- 
ing through  C,  the  water  vapor  in  the  gas  being  condensed  to  a 
great  extent.  Up  to  this  point  all  of  the  apparatus  is  necessary 
even  if  no  ammonia  recovery  is  attempted. 

For  a  gasification  capacity  of  less  than  30  tons  of  coal  in 
twenty-four  hours  it  is  not  usual  to  install  a  recovery  plant  on 
account  of  the  high  cost  of  installation.  Beyond  this  capacity 
the  installation  is  justified.  A  recovery  plant  consists  of  the 
acid  tower  E,  the  gas  cooling  tower  F,  and  the  air  heating  and 
saturating  tower  G  (see  Fig.  7-7). 

The  gas  after  leaving  the  condenser  C  enters  the  tower  E  at 
the  bottom  and  flows  upward  through  firebrick  checker  work. 
In  doing  so  it  meets  a  descending  rain  of  sulfuric  acid  liquor 
containing  about  4  per  cent  of  free  acid,  a^d  by  this  the  free 
ammonia  in  the  ascending  gas  is  fixed,  being  changed  to  sulfate. 
The  acid  liquor  is  circulated  by  a  special  pump,  and  kept 
at  the  proper  strength  by  drawing  off  the  sulfate  liquor  and 
adding  a  corresponding  amount  of  fresh  acid  solution  from  time 
to  time. 

The  gas  then  enters  the  cooling  tower  F,  at  the  bottom,  and 
in  its  ascent  is  cooled  by  descending  cold  water.  The  gas  gives 
up  its  burden  of  steam,  which  in  turn  heats  the  descending  cold 
water.  The  gas  is  then  conveyed  to  the  gas  mains. 

The  hot  water  leaving  the  gas-cooling  tower  is  pumped  to  the 
top  of  the  air-saturating  tower.  Here  it  flows  downward  through 
checker  work,  and  in  its  descent  saturates  and  heats  the  air, 
which  is  driven  upward  through  the  tower  by  blowers.  Leaving 
this  tower,  the  air-water  vapor  mixture  then  goes  to  the 
regenerator  B,  where  it  is  further  pre-heated  before  entering  the 
producer. 


GAS-ENGINE  FUELS 


165 


Sexton*  states  that  the  amount  of  steam  used  is  about  2i 
tons  per  ton  of  fuel,  and  estimates  that  about  two  tons  of  this 
go  through  undecomposed. 

The  method  has  the  advantage  that  slack  coal  may  be  gasified 
•with  success.  The  recovery  of  ammonia  amounts  to  about  1  ton 
for  23  tons  of  coal  gasified,  or  adding  the  fuel  required  for 
making  steam,  about  1  ton  for  28.5  tons  of  fuel. 

The  average  analysis  of  Mond  gas  is,  by  volume, 

11  per  cent  CO,  17.1  per  cent  C02,  1.8  per  cent  CH4,  .4  per  cent 
CMH2w  ,  27  per  cent  H,  and  42.5  per  cent  N. 

This  gas  is  free  from  tar  and  excess  of  moisture,  and  burns  with  a 
non-luminous  flame. 


FIG.  7-8.  —  Deutz  Suction  Producer. 

SUCTION  PRODUCERS.  —  Deutz.^  In  the  Deutz  suction  pro- 
ducer, Fig.  7-8,  the  vaporizer  is  arranged  around  the  top  of  the 
generator.  During  the  suction  stroke  of  the  engine,  fresh  air 
enters  the  vaporizer,  is  here  mixed  with  water  vapor,  and  then, 
flowing  through  the  connecting  pipe  at  the  left  side  of  the  genera- 
tor, reaches  the  under  side  of  the  grate.  The  gas  made  leaves  the 
generator  through  the  pipe  at  the  right  and  enters  the  wet  scrub- 
ber at  the  bottom.  From  here  it  passes  to  the  engine  through  a 

*  Sexton,  Producer  Gas,  p.  90. 
f  Giildner,  p.  386. 


166 


INTERNAL  COMBUSTION  ENGINES 


regulator.  Just  before  entering  the  engine  the  gas  passes  a  vessel 
containing  a  wire  brush  for  a  final  cleaning  of  tar.  The 
larger  Deutz  suction  installations  show  a  somewhat  different 
construction. 


FIG.  7-9.  —  Koerting  Suction  Producer. 

Koertmg*  Fig.  7-9  shows  a  Koerting  suction  plant  designed 
for  from  30-35  horse-power.  In  this  case  the  vaporizer  is  inde- 
pendent of  the  generator.  The  latter  is  heated  by  the  hot  gases 
on  their  way  to  scrubber  and  purifier.  During  the  heating-up 
period,  the  air  is  furnished  by  the  blower  shown.  The  smoke 
escapes  through  a  pipe  which  branches  off  beyond  the  vaporizer, 
so  that  this  will  be  heated  during  the  blowing-up  period. 


FIG.  7-10.  —  Koerting  Installation. 

A  complete  view  of  a  Koerting  plant  is  shown  in  Fig.  7-10. 
*  Giildner,  p.  386, 


GAS-ENGINE  FUELS 


167 


American  Crossley.  The  American  Crossley  suction  gas  plants 
in  this  country  are  built  by  the  Power  &  Mining  Machinery  Com- 
pany. Fig.  7-11  shows  a  complete  plant.  The  producer  is  of  con- 
ventional design.  The  fuel  bed  rests  on  a  shaking  grate.  The 
fuel  is  admitted  as  shown.  The  waste  heat  boiler  or  saturator 
surrounds  the  feed  tube.  The  water  level  in  this  saturator  is 
automatically  regulated.  During  the  firing-up  period  the  pro- 
ducer is  blown  by  means  of  the  fan  shown,  the  gases  escaping  by 
the  purge  pipe.  A  new  idea  seems  to  be  the  saturating  of  only 
part  of  the  air  supply.  The  makers  point  out  the  difficulty  of 


FIG.  7-11.  —  American  Crossley  Producer. 

making  uniform  gas  at  all,  especially  at  low,  loads,  owing  to  the 
difficulty  of  controlling  the  amount  of  steam  admitted.  To 
remedy  this,  part  of  the  air  only  passes  through  the  saturator, 
while  the  rest  is  directly  admitted  to  the  ash  pit.  Valves  on  these 
two  air  inlets  can  be  set  so  as  to  give  satisfactory  gas  over  wide 
ranges  of  load. 

Another  arrangement  in  which  this  producer  plant  differs  from 
most  others  is  that  of  the  cleaning  apparatus.  This  consists  of 
a  wet  scrubber,  an  hydraulic  box,  and  a  combination  wet  and  dry 
scrubber.  The  gas  enters  the  first  and  passes  downward,  passing 
upward  in  the  combination  scrubber.  The  operation  is  shown 
plainly  in  the  cut. 


168 


INTERNAL  COMBUSTION  ENGINES 


Fairbanks-Morse.  Fig.  7-12  shows  a  Fairbanks-Morse  installa- 
tion for  21  horse-power,  the  producer  itself  being  shown  in  Fig. 
7-13,  in  greater  detail.  The  general  design  of  the  producer  is  very 


FIG.  7-12.  —  Fairbanks-Morse  Installation. 

similar  to  that  of  the  American-Crossley,  except  that  all  of  the 
air  passes  through  the  vaporizer.  Apparently  only  a  wet  scrub- 
ber is  provided,  it  being  evidently  intended  to  use  anthracite 
only.  A  gas. tank  of  considerable  volume  is  interposed  between 
scrubber  and  engine. 

The  suction  producers  so  far  described  have  been  for  anthra- 
cite, coke,  or  charcoal.  The  desire  to  utilize  soft  coal,  lignites, 
etc.,  has  led  to  special  designs,  of  which  the  following  are  a  few 
examples.  In  some  of  these  all  of  the  gas  made  from  the  fuel 
is  passed  through  other  highly  incandescent  but  gas-free  fuel  to 
fix  the  tar-forming  gases,  in  others  only  the  gases  of  distillation 
are  so  treated. 


GAS-ENGINE  FUELS 


169 


FIG.  7-13.  —  Fairbanks'  Producer. 

Riche.  *     Riche's  producer,  Fig.  7-14,  is  especially  designed 
for  wood,  but  it  may  also  be  used  for  hard  coal  and  coke.    The 


FIG.  7-14.  —  Riche's  Producer. 
*  Genie  Civil,  1901-2,  p.  398. 


170 


INTERNAL  COMBUSTION  ENGINES 


column  at  the  right  serves  as  a  magazine  for  the  fuel  bed  at  b. 
The  gases  formed  are  sucked  up  through  C,  which  is  kept  filled 
with  incandescent  charcoal.  The  fixed  gas  passes  through  pipes 
d  and  e,  being  washed  by  means  of  sprayed  water  in  its  passage. 
Lencauchez.  *  Instead  of  using  two  separate  stacks,  the  two 
fuels  may  be  put  together  in  one  furnace,  as  is  done  by  Lencauchez, 
Fig.  7-15.  Long-flaming  bituminous  coal  is  charged  through  a, 
while  through  6  coke  from  coke  ovens  or  gas  works  is  charged. 
Water  is  evaporated  in  the  ash  pit.  The  openings  c  and  d  show 
only  black  smoke,  while  e  shows  a  colorless  gas.  The  gases  from 
the  soft  coal  are  fixed  in  passing  through  the  incandescent  coke 
layer.  Schottler  mentions  that  this  gas  is  not  used  as  power 


FIG.  7-15.  —  Lencauchez  Producer. 

gas  but  for  heating  purposes.     The  proportions  of  the  charge  are 
about  20-25  per  cent  coke  to  80-75  per  cent  soft  coal. 

Lencauchez.  f  Another  way  of  reaching  the  same  end,  that  is, 
fixing  the  tarry  gases,  is  by  the  use  of  so-called  double  genera- 
tors. In  these  generators  the  charge  burns  both  top  and  bottom, 
the  gases  being  drawn  off  at  about  the  middle  of  the  producer. 
Fig.  7-16  shows  a  generator  of  this  type  designed  by  Lencauchez. 
It  consists  essentially  of  three  conical  parts.  The  upper  one 
serves  as  a  magazine.  In  the  middle  one  the  fire  burns  on  top, 
in  the  bottom  one  at  the  bottom.  Air  enters  at  D  and  B.  Water 
is  introduced  at  A  and  evaporated  in  the  ash  pit.  The  air  and 
gas  currents  are  shown  by  the  arrows.  The  gases  of  distillation 
formed  in  the  magazine  are  drawn  downward  through  the 
*  Zeitschrift  des  Vereins  deutscher  Ingenieure,  1905,  p.  1903. 
f  Zeitschrift  des  Vereins  deutscher  Ingenieure,  1905,  p.  1905 


GAS-ENGINE  FUELS 


171 


FIG.  7-16.  —  Lencauchez  Double  Zone  Generator. 

incandescent  fuel  in  the  middle  section  and  are  so  fixed.  Any 
unburned  coked  fuel  then  passes  on  toward  the  grate  and  is 
gasified  on  reaching  the  incandescent  zone  in  the  lower  section. 


FIG.  7-17.  —  Koerting  Producer  for  Peat. 


172 


INTERNAL  COMBUSTION  ENGINES 


Koerting.  *  Koerting's  producer  for  peat,  Fig.  7-17,  is  built 
along  lines  similar  to  the  above.  The  producer  consists  of  two 
parts,  of  which  the  upper  and  larger  one  is  fitted  with  step  grates, 
a  a,  the  lower  one  with  an  ordinary  grate  b.  When  in  operation, 
the  charge  of  peat  in  the  upper  parts  burns  only  near  the  grates 
a  a,  while  the  inner  core  of  peat  is  only  coked.  The  gases  so 
formed  pass  into  the  perforated  pipe  c  and  are  led  through  d 
under  the  grate  b.  The  coked  peat  formed  in  the  upper  part 
passes  downward  arid  is  gasified  over  the  grate  b.  The  gases 
from  d  pass  through  the  incandescent  layer  above  6,  are  fixed,  and 
together  with  the  gases  formed  over  b  f  ass  out  at  e.  One  would 
naturally  assume  at  first  sight  that  the  gases  of  distillation  would 
pass  directly  downward  and  out  at  e,  instead  of  entering  c  and 
passing  through  d.  The  direction  of  the  movement  is  regulated 
by  creating  a  slight  vacuum  under  the  grate  b,  and  by  contract- 
ing the  producer  section  at  /.  This  contraction  produces  an  extra 
resistance  to  the  passage  of  gases  downward,  and  they  conse- 
quently take  the  more  convenient  way  through  c  and  d.  Schottler 
gives  the  analysis  of  a  peat  gas  so  made  as 
14  per  cent  C02,  4  per  cent  CH4,  15  per  cent  CO,  10  per  cent  H, 

and  57  per  cent  N, 
producer  efficiency  being  about  75  per  cent. 


FIG.  7-18.  —  Crossley  Producer. 
*  Zeitschrift  des  Vereins  deutscher  Ingenieure,  1905,  p.  1909. 


GAS-ENGINE  FUELS 


173 


COMBINATION  SYSTEMS.  —  Crossley.  The  Crossley  producer, 
Fig.  7-18,  is  suitable  for  bituminous  coal,  or  other  fuel  high  in 
volatile  matter.  The  fuel  is  first  charged  into  the  retorts  A,  and 
is  there  distilled  by  the  sensible  heat  of  the  gases  formed  below. 
When  charging,  the  valve  B  is  drawn  tightly  against  its  seat,  and 
the  fuel  is  projected  downward  by  turning  the  spiral  D  by  means 
of  the  capstan.  When  the  distillation  is  complete  the  casting  B  is 
lowered  and  the  coked  fuel  is  thrown  into  the  main  part  of  the 
producer  by  turning  D.  At  the  same  time  it  is  broken  up  by 
the  spirals.  The  gases  of  distillation  are  drawn  out  of  the 
retorts  through  the  pipe  F,  and  pass  under  the  grate  T7,  at  M. 
The  suction  is  produced  by  a  fan  blower,  which  at  the  same  time 
draws  air  and  steam  to  the  main  bed  of  fuel,  and  discharges  the 
resulting  producer  gas  into  a  holder  at  suitable  pressure. 


FIG.  7-19.  —  Deutz  Double  Zone  Producer. 

Deutz.  The  Deutz  plant  for  bituminous  coal  is  shown  in 
Fig.  7-19.  The  producer  is  of  the  double-generator  type.  The  air 
enters  the  vaporizer  at  a,  and  reaches  the  ash  pit  through  pipe  b. 
The  fire  burns  top  and  bottom.  Green  coal  is  charged  at  the  top. 
It  is  distilled,  the  gases  formed  pass  downward  through  incan- 
descent fuel  and  are  so  fixed,  passing  out  at  c.  The  greater  part 
of  the  fuel  coked  near  the  top  passes  downward  and  is  finally 
gasified  in  the  lower  part  of  the  producer,  the  gases  also  passing 
out  at  c.  Suction  is  maintained  by  a  fan  connected  beyond  the 
coke  scrubber.  Owing  to  the  fixing  of  the  tarry  gases  it  is  found 


174 


INTERNAL  COMBUSTION  ENGINES 


that  a  coke  scrubber  is  all  that  is  required.  The  fan,  which  is 
almost  a  necessary  part  of  such  a  plant,  owing  to  the  increased 
friction  entailed  by  the  design  of  the  producer,  delivers  the  gas 
to  a  holder.  The  holder  regulates  the  make  of  gas  by  controlling 
the  fan.  During  the  firing-up  period,  a  purge  pipe  is  lowered 
over  the  top  of  the  generator,  which  has  no  special  charging  bell. 
The  same  fan  is  then  used  as  a  blower  to  furnish  air  to  the  pro- 
ducer, by-passing  the  scrubber. 


FIG.  7-20.  —  Loomis-Pettibone  Producer. 

Loomis-Pettibone.  *  The  Loomis-Pettibone  gas  apparatus,  Fig. 
7-20,  may  be  used  for  the  making  of  producer  gas  alone,  or  for 
alternate  manufacture  of  water  gas  and  lean  power  gas.  Each 
plant  consists  of  two  producers,  a  boiler,  a  combination  wet  and 
dry  scrubber,  and  an  exhauster  which  delivers  the  gas  made  to 
the  proper  holder  or  the  purge  pipe,  depending  upon  the  positions 
of  the  valves  x,  y  and  z.  The  producers  are  charged  through  the 
top.  Through  the  same  doors  the  air  also  enters.  Thus  the 
gases  pass  downward  through  incandescent  fuel,  so  that  any  kind 
of  fuel  may  be  employed.  Leaving  the  producers  at  the  bottom, 
the  gases  pass  through  the  boiler,  where  they  are  cooled,  and 
then  through  the  scrubber  and  purifier.  The  make  of  gas  is  con- 
trolled by  the  speed  of  the  exhauster,  the  suction  pressure  being 
ordinarily  from  12  to  24  inches,  the  delivery  pressure  about  6 
inches  of  water. 

Suppose  it  is  desired  to  make  water  gas.  The  feed  doors  E 
*  The  Power  Plant  of  the  Montezuma  Copper  Co.,  John  Langton. 


GAS-ENGINE  FUELS  175 

and  F,  and  the  valve  B,  are  closed.  Steam  is  then  admitted 
under  the  grate  of  producer  No.  2,  the  right-hand  producer  in 
Fig.  7-20.  The  water  gas  formed  in  No.  2  is  passed  through  the 
top  connection  to  No.  1,  passes  down  No.  1,  out  at  A,  and  thus 
up  the  boiler  and  through  the  scrubber  to  gas  holder.  The  next 
time  water  gas  is  run,  the  directions  are  reversed,  or  this  may  be 
done  when  one  half  of  a  water-gas  run  is  completed.  To  make 
water  gas,  the  aim  is  to  blow  the  producers  up  with  air  as  hot  as 
possible,  and  then  pass  steam  only  through  them  until  a  great 
deal  of  it  goes  through  undecomposed.  Then  air  alone  is  again 
used  to  get  the  fires  hot.  This  procedure  means  a  wide  range  of 
temperature  in  the  producer,  and  while  this  does  not  affect  the 
quality  of  the  water  gas  seriously,  it  does  affect  the  producer 
gas  made  during  the  blowing-up  periods,  as  a  great  deal  of  CO2 
is  formed  when  the  producers  are  comparatively  cool.  In  a  large 
plant  where  several  producers  are  at  one  time  delivering  to  the 
same  gas  holder,  this  irregularity  is  not  much  felt  at  the  mixing 
valve  of  the  engine  where  the  two  gases  are  mixed  in  proper 
proportion.  For  a  single  set  plant  this  feature  of  varying  pro- 
ducer gas  make  is  more  serious,  and  for  this  case  the  producers 
may  be  operated  in  a  different  manner. 

To  this  end  the  steam  connections,  M,  are  used  so  that  steam 
may  be  introduced  along  with  the  air,  thus  making  water  gas 
and  lean  gas  concurrently,  maintaining  the  producer  tempera- 
ture fairly  constant  for  a  long  time;  in  other  words,  true  producer 
gas  is  made.  To  get  around  the  too  fine  adjustment  of  air  and 
steam  for  constant  temperature,  somewhat  less  top  steam  than 
could  be  used  is  employed,  thus  allowing  the  temperature  to 
slowly  rise.  A  short  water-gas  run  brings  it  down  again  to  the 
proper  point.  The  water  gas  made  is  slowly  fed  from  its  holder 
to  the  main  gas  holder  through  a  controlled  throttle  valve  so  that 
its  rate  of  feeding  approximately  equals  its  rate  of  production. 

4.  Some  Producer  Details.  -  -  Mathot,  in  The  Engineering 
Magazine,  May,  1905,  gives  the  following  data  for  suction  por- 
ducers : 

To  get  the  greatest  production  of  H  and  the  most  effective 
reduction  of  CO2,  make  the  cross-section  of  the  base  of  the  pro- 
ducer from  0.6  to  0.9  of  the  piston  area  of  the  engine.  This  is 
for  a  single  cylinder  4-cycle  engine  at  from  600-800  feet  piston 


176  INTERNAL  COMBUSTION  ENGINES 

speed.  The  depth  of  fuel  bed  should  be  from  3  to  5  times  the  diam- 
eter at  the  base,  for  £-inch  to  f-inch  lump  coal.  Amount  of 
water  dissociated  is  from  0.8  to  1.2  times  the  weight  of  coal  con- 
sumed. 

More  than  twenty  analyses  give  the  following  average  figures: 

CO,  24  per  cent;  CO2,  5  per  cent;  H,  17  per  cent;  N,  54  per  cent. 

Calorific  power  from  135  to  150  B.  T.  U.  per  cubic  foot.  Average 
coal  used  shows  89  per  cent  C,  2  per  cent  H,  4  per  cent  O  +  N, 
and  5  per  cent  ash.  Best  size  coal  is  from  J-inch  to  1^-inch  lump 
with  8  to  10  per  cent  of  ash,  and  not  more  than  8  to  10  per  cent 
volatile  matter. 

Water  in  the  ash  pan  is  satisfactory  for  steam  production  if 
the  air  is  pre-heated.  But  preference  is  now  given  to  internally 
heated  vaporizers.  Tubular  vaporizers  produce  sufficient  steam 
after  10  to  13  minutes.  With  well-designed  apparatus,  any  suc- 
tion plant  should  be  in  operation  25  minutes  after  lighting  up. 

The  volume  of  the  scrubber  should  be  from  6  to  8  times  that  of 
the  producer.  Its  height  should  be  from  3  to  4  times  its  diameter. 
The  filling  is  coke  in  pieces  3  to  4  inches  in  diameter,  the  coarser 
pieces  near  the  bottom,  the  smaller  near  the  top.  Amount  of 
water  used  for  washing  is  from  3  to  5  gallons  per  horse-power  per 
hour  for  anthracite  gas. 

According  to  the  DeLavergne  Company,  the  impurities  to  be 
removed  from  one  ton  of  fuel  are,  for  anthracite,  from  1  to  2  pounds 
of  ammonia,  traces  of  sulfur,  and  from  5  to  10  pounds  of  tar; 
for  bituminous  coal,  from  4  to  5  pounds  of  ammonia,  sulfur  from 
traces  to  5  per  cent,  and  from  10  to  12  gallons  of  tar. 

The  Morgan  Construction  Company  point  out  the  effect  of 
sulfur  on  the  formation  of  clinker.  A  coal  with  a  large  per 
cent  of  ash  may  work  satisfactorily  in  a  producer  provided  the 
sulfur  does  not  exceed  1  per  cent.  Above  3  per  cent  the  effect 
of  sulfur  in  forming  clinker  is  badly  felt  unless  special  facilities 
are  at  hand  to  break  up  such  formations. 

The  same  company  makes  the  following  statements  regard- 
ing pressure-producer  capacities.  The  best  rate  of  combustion 
seems  to  be  about  10  pounds  of  bituminous  coal  per  square  foot 
cross-section  per  hour,  the  coal  carrying  10  per  cent  of  ash  and 
1£  per  cent  of  sulfur.  With  coals  of  lower  ash  content  the  rate 


I 

GAS-ENGINE  FUELS  177 

may  be  increased  to  12  pounds,  and  in  some  special  cases  to  15 
pounds.  For  poorer  coals,  however,  the  rate  may  sink  to  6  or  8 
pounds.  Regarding  the  size  of  gas  flues  and  pipes,  the  statement 
is  made  that  each  square  foot  of  gas  flue  will  take  care  of  a  gasifica- 
tion of  200  pounds  of  coal  per  hour,  and  will  serve  a  gas-making 
area  of  16  square  feet  in  the  producer. 


t 


CHAPTER  VIII 

THE  GAS-ENGINE  FUELS'.  LIQUID  FUELS,  CARBURETER  AND 
VAPORIZERS 

i.  The  Crude  Oils  and  their  Distillates.  —  The  crude 
petroleum  oils  are  practically  mechanical  mixtures  of  various 
hydrocarbon  families.  It  is  therefore  to  be  expected  that  crude 
oils  from  various  fields  show  compositions  considerably  different. 
From  these  crude  oils  we  obtain  by  distillation  all  of  the  mineral 
oils  now  so  widely  used  for  a  great  variety  of  purposes.  Of  these 
oils  the  various  gasolines,  kerosenes,  and  the  so-called  "distillates, " 
besides  crude  oil  itself,  are  used  for  gas-engine  fuels. 

CRUDE  OIL. — The  following  table*  gives  a  few  analyses  of  crude 
oils  from  different  parts  of  the  world.  These  oils  are  usually  of 
a  dark  green  color,  the  specific  gravity  is  between  0.80  to  0.90 
at  32  degrees,  and  the  flash  point  between  76  and  93  degrees 
Fahrenheit. 


Sp. 
Gravity 
at  32° 

C 

H 

Oand 
Impuri- 
ties 

Lower 
Heating  Value 
per  pound 

Heavy  crude  W.  Virginia  

.873 

.841 
.886 
.826 
.886 

83.5 
84.3 
84.9 
82.0 
84.9 

13.3 
14.1 
13.7 
14.8 
13.7 

3.2 
1.6 
1.4 
3.2 
1.4 

18324 
18400 
19210 
17930 
19210 
19463 
20410 
21600 
18781 
18010 
18416 
19440 
19496 
18330 

Light  crude  W.  Virginia  
Heavy  crude  Pa. 

Light  crude  Pa 

Heavy  crude  Ohio  

Salt  Creek,  Wyoming  
Bothwell,  Canada   

.857 

.861 
.872 
.885 
.884 
.956 

84.3 
80.2 
86.2 
82.2 
85.3 
86.3 
86.6 
85.0 

13.4 
17.1 
13.3 
12.1 
12.6 
13.6 
12.3 
11.2 

2.3 

2.7 
.5 
5.7 
2.1 
.1 
.1.1 
2.8 

Lima,  Ohio  

Schwabwjller,  Lower  Rhine  .  .  . 
Gallicia  East 

Gallicia,  East  

Light  Crude  Baku    

Heavy  Crude  Baku 

Keudong  Java    

*  Poole,  the  Calorific  Power  of  Fuels. 
178 


GAS-ENGINE    FUELS  179 

GASOLINE.  —  After  the  distillation  of  the  very  light  products 
from  crude  oil,  we  obtain  a  series  of  gasolines  of  varying  flash 
points  and*  gravity.  The  first  of  these  is  86  degree  gasoline,  as 
measured  on  the  Beaume  scale.  This  forms  a  mixture  with  air 
so  readily  even  at  ordinary  temperature  that  it  is  somewhat 
dangerous  and  not  often  used.  The  next  gasoline,  the  original 
liquid  gas-engine  fuel,  is  74-degree  gasoline.  Owing  to  the  much 
greater  consumption  of  gasoline,  due  to  the  introduction  of  the 
automobile  mainly,  the  gravity  of  gasoline  and  also  the  flash 
point  have  slowly  gone  up,  until  to-day  69-degree  gasoline  is 
quite  common.  , 

Gasoline  vaporizes  readily  at  ordinary  room  temperatures, 
and  it  is  therefore  necessary  to  keep  it  covered,  not  only  to  pre- 
vent loss  but  also  accidents  due  to  explosions.  Insurance  com- 
"panies  usually  specify  that  any  quantity  of  it  must  be  kept  in 
••an  underground  tank  outside  of  the  building,  and  that  13 
undoubtedly  the  best  way. 

Data  on  the  heating  value  of  gasoline  is  not  at  all  plentiful. 
A  sample  the  writer  had  the  opportunity  of  testing  recently  gave 
the  following  figures: 
f  Specific  gravity,  Beaume  69.5  at  60  degrees  Fahrenheit. 

Composition,  84.76  per  cent  C,  15.24  per  cent  H. 

Lower  heating  value  as  computed  from  analysis,  20411  B.  T.  U. 

Heating  value  as  determined  by  Junker's  calorimeter,  higher 
value  19606,  lower  value  18482  B.  T.  U. 

tf  f  It  should  be  noted  that  this  is  one  of  the  instances  where  the 
heating  value  as  computed  is  much  higher  than  the  actual  value, 
nearly  2000  B.  T.  U.  =  10  f)er  cent  in  this  case.  It  shows  the 
necessity  of  calorimetric  determination  for  accurate  work. 

J^EROSENE.  —  Kerosene,  the  next  heavier  distillate  beyond 
gasolines,  is  not  as  extensively  used  as  gasoline  in  this  country 
for  gas  engines.  It  will  not  form  an  explosive  mixture  with  air 
at  ordinary  temperatures,  and  therefore  requires  more  elaborate 
apparatus  for  the  formation  of  such  a  mixture^  The  following 
data  is  given  by  Mr.  S.  A.  Moss  for  ordinary  American  kerosene: 

Sp.  Gr.  at  60°        Flash  point       C       H      Lower  Heating  Value 

open  by  weight        per  Ib.  B.  T.  U. 

.80  100°  .85      .15  18520 


180 


INTERNAL  COMBUSTION  ENGINES 


Specific  gravity  at  24°C 

Average  composition,  C 

H 

O 


Further  reliable  data  on  kerosene  is  given  in  a  lecture  by 
Diesel  in  1897,  in  connection  with  Schottler's  test  of  the  Diesel 
engine. 

(75.2°  F.)    .789. 
85.13  per  cent. 
14.21  per  cent. 
.66  per  cent. 

Lower  heating  value  computed  from  analysis,  19874  B.  T.  U. 
Lower  heating  value  by  Junker's  calorimeter, 

average  of  five  tests,  18242  B.  T.  U. 

DISTILLATES.  —  A  distillation  product  resembling  kerosene 
in  its  general  properties  is  sometimes  used  as  fuel.  These  so- 
called  distillates  are  not  as  well  refined  as  kerosene,  but  are  handled 
the  same  when  used  for  engine  work. 

The  following  table,  due  to  Hofer  and  transposed  from  Giild- 
ner,  shows  a  good  method  of  presenting  the  various  distillation 
products  from  crude  oil: 

(a)  Volatile  Oils. 

SP.  GR.,  .65-. 75,  FLASH  POINT  BELOW  70°  F.,  BOILING-POINT 
BELOW  300° 


Sp.  Gr. 

Boiling-Point 

Petroleum  Ether                                    .  .  . 

65-.  66 

95°-  122°  F. 

Benzine 

66-  68 

112°-  158° 

Various  Gasolenes    

.67-.  74 

149°-300° 

(b)  Illuminating  Oils. 

SP.  GR,,  .78-.S6,  FLASH  POINT  70°-158°,  BOILING-POINT 
ABOVE  300°  F. 


Sp.  Gr. 

American  Kerosene  

.  .  .  78  -.81 

Russian  Kerosene 

.    .      .82-825 

Standard  White 

808-  812 

Prime  White  

80  -.806 

Astralin  . 

.85  -.86 

GAS-ENGINE  FUELS  181 

(c)  Heavy  Oils. 

SP.  GR.,  .8G-.96,  FLASH  POINT  374-482°  F. 

Sp.  Gr. 

Solar  Oil    86-.8S 

Lubricating  and  Cylinder  Oils.     .88-.90,  etc.,  can  be  used  as  lubricating  oils 

only. 

2.  Alcohol.  —  The  use  of  alcohol  as  a  gas-engine  fuel  in  this 
country  is  as  yet  of  no  great  importance,  although  the  recent 
action  of  Congress  in  removing  internal  revenue  under  certain 
restrictions  will  do  a  great  deal  toward  helping  alcohol  to  the 
place  it  deserves  as  a  fuel.  In  some  European  countries,  Germany 
for  instance,  the  price  of  alcohol  is  not  much  greater  than  that 
of  gasoline,  and  it  may  therefore  compete  with  gasoline  with  some 
success,  especially  when  some  of  its  advantages  are  considered. 
It  is  much  safer  than  gasoline  as  regards  fire  risks,  and  since 
it  always  contains  some  water,  a  higher  degree  of  compression 
may  be  employed  in  the  engine,  guaranteeing  better  thermal 
efficiency.  These  advantages  compensate  largely  the  greater  spe- 
cific heat  cost  of  alcohol. 

Ethyl  alcohol,  *  whose  chemical  formula  is  C2H6O,  may  be 
made  in  various  ways,  but  the  commercial  alcohol  of  to-day  is 
the  result  of  fermentation,  generally  of  grape  sugar,  in  the  final 
stage.  The  raw  materials  are  various.  Thus,  according  to 
Sand  f  they  may  be  divided  into  three  classes: 

1.  Those  containing  starch  —  potatoes,  with  15  to  24  per  cent 

starch, 
rye,  with  50  to  56  per  cent 

starch, 
corn,  with  60  per  cent  starch, 

2.  Those  containing  sugar  —  sugar  beet,   with  8  to   18  per 

cent  sugar, 

sugar  cane,  with  12  to  16  per 
cent   sugar. 

3.  Those  containing  alcohol — wine  with  9  to  16  per  cent  alcohol. 

*  What  follows  is  a  reprint  from  an  article  by  the  writer  on  the  use  of 
alcohol  as  a  fuel  for  gas  engines  in  Marine  Engineering,  June,  1906. 

f  Sand,  Zeitschrift  des  Vereines  deutscher  Ingenieure,  1894,  p.  933. 


182  INTERNAL  COMBUSTION  ENGINES 

The  method  of  manufacture,  of  course,  varies  with  the 
raw  material,  but  need  not  be  described  in  detail  here.  Theo- 
retically, 100  pounds  of  grape  sugar  should  yield  51  pounds 
of  pure  alcohol;  in  reality  the  yield  is  from  £  to  $  less  than  this 
amount. 

A  second  method  of  producing  alcohol,  notably  mentioned 
by  Witz  in  his  "Moteurs  a  Gaz  et  a  Petrole,"  is  to  start  with 
calcium  carbide  as  a  raw  material.  This,  by  a  somewhat  com- 
plicated process,  can  be  changed  from  CaC2  through  the  stages 
of  C2H2  and  C2H4  to  alcohol,  C2H6O.  Barium  carbide  or  strontium 
carbide  can  be  used  in  the  same  way.  Witz  states  that  from  1 
kilogram  (2.2  pounds)  of  calcium  carbide  0.8  liter  (1.69  pints) 
of  alcohol  can  be  obtained;  this  is  equivalent  to  0.096  United 
States  gallons  of  alcohol  from  1  pound  of  carbide.  Estimating 
the  price  of  carbide  at  3  cents  per  pound,  which  is  even  now  some- 
what below  the  market  price,  1  gallon  of  alcohol  would  therefore 
cost,  in  raw  material  alone,  31.2  cents,  to  say  nothing  of  the  cost 
of  the  chemical  operations.  The  by-products  in  the  case  of  the 
calcium  carbide  do  not  amount  to  much.  There  is  consequently 
little  likelihood  that  the  so-called  synthetic  or  mineral  alcohol 
will  ever  seriously  compete  with  gasoline  or  kerosene  for 
power. 

The  heating  value  of  alcohol  cannot  be  accurately  computed 
from  its  chemical  composition,  because  nothing  definite  is  known 
of  the  arrangement  of  the  atoms  entering  the  composition.  We 
therefore  have  to  depend  upon  the  calorimeter.  The  figures 
determined  for  absolute  alcohol  by  various  experimenters  are 
as  follows: 


Higher  Heating  Value 
per  pound 

Lower  Heating  Value 
per  pound 

Thomson 

13310  B  T  U. 

12036  B.  T.  U. 

Favre  &  Silberman    

12913  B.  T.  U. 

11664  B.  T.  U. 

The  value  11664  B.  T.  U.  is  the  one  most  generally  used. 
Absolute  alcohol  has  a  specific  gravity  of  0.7946  at  15  degrees 
Centigrade  (59  degrees  Fahrenheit),  so  that  one  gallon  of  pure 
alcohol  weighs  6.625  pounds,  and  has  a  lower  heating  value  of 
77274  B.  T.  U. 


GAS-ENGINE  FUELS 


183 


One  pound  of  C2H6O  contains  0.522  pound  carbon,  0.130  pound 
hydrogen,  and  0.348  pound  oxygen. 

According  to  this  there  will  be  required  for  the  combustion 
of  one  pound  of  absolute  or  100  per  cent  alcohol, 


(0.522  X  2.66)+  (0.130  X  8)  -  0.348 
0.23 


=  9  pounds  of  air. 


This  is  the  equivalent  of  111.5  cubic  feet  of  air  at  62  degrees 
Fahrenheit,  per  pound  of  C2H6O.  Commercial  alcohol,  however, 
is  never  pure,  but  nearly  always  contains  a  certain  quantity  of 
water,  the  admixture  being  measured  according  to  volume  per 
cent.  Thus,  90  per  cent  alcohol  means  that  the  mixture  carries 
10  per  cent  by  volume  of  water.  The  heating  value  of  such 
alcohol  is  of  course  correspondingly  reduced  from  that  of 
100  per  cent  alcohol  according  to  the  following  table,  due  to 
Schottler: 


Absolute  alcohol 
volume  —  per  cent 

Specific 
gravity 

Absolute  alcohol 
weight  —  per  cent 

Lower 
heating 
value  per 
pound 
B.  T.  U. 

95 

0.805 

93.8 

10880 

90 

0.815 

87.7 

10080 

85 

0.826 

81.8 

9360 

80 

0.836 

76.1 

8630 

75 

0.846 

70.5 

7920 

70 

0.856 

65.0 

7200 

70 

0.856 

65.0 

7200 

It  is  required  by  law,  in  countries  where  alcohol  is  now  used 
in  the  industries,  to  so  fix  the  fuel  that  it  is  rendered  undrinkable. 
This  process  is  called  "  denaturizing "  the  alcohol.  The  bill 
passed  by  Congress  at  the  last  session  provides  for  the  same 
thing.  The  materials  used  for  this  purpose  differ  in  the  various 
European  countries.  Some  of  them  try  to  keep  the  process  a 
secret,  hence  some  of  the  information  given  in  the  following  table  * 
is  based  upon  analyses. 

*  Zeitschrift  des  Vereines  deutscher  Ingenieure,  June,  1905. 


184  INTERNAL  COMBUSTION  ENGINES 

MATERIALS  USED  TQ  DENATURIZE  ETHYL  ALCOHOL 


Country 

Sp.  Gr.  of 
Denat- 
urized 
Alcohol 
at 
15° 
C 

Methylene 
(wood 
alcohol) 
and 
its 
impurities 
per  cent 

Pyridine 
or 
Pyridine 
Bases 
per  cent 

Ace- 
tone 
per  cent 

Benzol 
per  cent 

Benzine 
per  cent 

France   

0.832 

7.5 



2.5 



0.5 

Germany 
Denat.  Alcohol.  . 

0.819 

1.5 

0.5 

0.5 

Motor  Alcohol  .  . 

0.825 

0.75 

0.25 

0.25 

2.0 

— 

Austria 

Denat.  Alcohol.  . 

0.835 

3.75 

0.5 

1.25 

— 

— 

Motor  Alcohol  .  . 

0.826 

0.5 

trace 

trace 

2.5 

— 

Russia    

0.836 

10.0 

0..5 

5.0 

— 

— 

Italy 
Motor  Alcohol  .  . 

0.835 

6.5 

0.65 

2.0 

1.0 

Switzerland  

0.837 

5.0 

0.32 

2.2 

— 

•  —  • 

It  will  be  noted  from  the  table  that  the  material  most  used 
for  denaturizing  ethyl  alcohol  is  wood  alcohol.  The  heating 
value  of  the  fuel  is  by  the  addition  of  the  denaturizing  liquid 
changed  but  little  in  most  cases. 

Benzol,  C6H6,  besides  being  used  for  denaturizing,  is  some- 
times used  in  larger  quantities  than  indicated  in  the  above  table, 
for  the  purpose  of  increasing  the  heating  value  of  the  fuel  mixture 
per  pound.  Benzol  has  a  specific  gravity  of  0.866  and  a  heating 
value  of  17190  B.  T.  U.  per  pound.  A  mixture  of  x  per  cent 
by  weight  of  absolute  alcohol  with  y  per  cent  of  benzol,  will  there- 
fore have  a  heating  value  of 

[11664  x  +  17190  y]  B.  T.  U.  per  Ib. 

If  the  alcohol  is  not  absolute,  its  proper  heating  value  should 
be  substituted  from  the  table  above  given.  In  this  way  from 
10  to  40  per  cent  of  benzol  is  sometimes  employed,  thus  raising 
the  heating  value  of  the  fuel,  and  at  the  same  time  decreasing 
the  specific  heat  cost,  i.e.,  the  cost  per  heat  unit. 

There  is  a  second  reason  why  benzol  is  employed.  Under  cer- 
tain circumstances  there  will  be  formed  acetic  acid  in  the  products 
of  combustion  of  alcohol.  This  causes  rusting  of  the  engine  parts. 
On  examination  it  will  be  found  that  this  is  due  to  a  combustion 


GAS-ENGINE  FUELS  185 

with  insufficient  air  supply,  and  the  surest  way  to  prevent  rust- 
ing, therefore,  is  to  use  a  good  excess  of  air,  and  to  have  a  perfect 
mixture.  Under  such  conditions  there  will  be  no  danger  of  cor- 
rosion. It  is  also  found  that  a  good  addition  of  benzol  acts  as  an 
additional  safeguard.  It  should  not  be  forgotten  in  this  connec- 
tion, however,  that  the  great  advantage  possessed  by  alcohol  in 
its  odorless  exhaust  is  sacrificed  to  some  extent  by  the  use  of  ben- 
zol. 

3.  Mixing  Devices  for  Liquid  Fuels.  —  As  has  been  already 
pointed  out,  the  fuel  mixture  of  a  gas  engine  is  always  a  gas  or 
vapor  mixed  with  air.  Hence  in  the  case  of  liquid  fuels  special 
devices  are  required  to  convert  these  fuels  into  gases  or  vapor. 
Such  devices  are  indiscriminately  known  as  carbureters,  vapor- 
izers, mixers,  or  mixing  valves.  In  the  strict  sense,  a  carbureter 
is  a  device  in  which  the  mixture  is  formed  by  passing  air  over  or 
through  the  liquid  fuel.  When  no  special  heating  of  the  fuel  is 
done,  these  devices  are  applicable  to  the  more  volatile  fuels  only, 
as  gasoline.  The  name  carbureter,  however,  is  also  used  when  in 
this  device  gasoline  is  mechanically  atomized  or  sprayed  into  the 
current  of  incoming  air.  The  term  vaporizer  is  usually  employed 
when  considerable  heat  for  gasification  or  vaporization  is  re- 
quired, as  is  the  case  for  kerosene,  crude  oil,  and  alcohol. 

MIXING  DEVICES  FOR  GASOLINE:  CARBURETERS.  —  Carbu- 
reters in  which  the  air  is  passed  over  or  through  gasoline  have 
the  drawback  that  when  the  carbureter  chamber  is  filled  with 
fresh  gasoline  the  lighter  constituents  of  the  liquid  distil  off 
first.  The  parts  harder  to  vaporize  remain  behind,  so  that  the 
fuel  mixture  is  anything  but  constant,  growing  leaner  as  the 
vaporization  progresses. 

Atomizing  or  spraying  carbureters  are  not  open  to  this  objec- 
tion, a  definite  amount  of  gasoline  being  injected  each  time. 
Hence  they  are  much  used*,  especially  in  automobile  work. 

Figure  8-1  shows  a  carbureter  which  is  of  what  has  been  very 
aptly  termed  the  bubbling  type.  The  suction  stroke  of  the 
engine  establishes  a  partial  vacuum  in  a  through  the  check 
valve  e,  and  the  chamber  d,  interposed  for  reasons  of  safety. 
This  causes  air  to  enter  through  the  screen  6,  rising  through  c  in  a 
spray.  Bubbling  up  through  the  gasoline  it  carries  with  it  some 
of  the  vaporized  liquid  and  goes  through  d  and  e  to  the  engine, 


186 


INTERNAL  COMBUSTION   ENGINES 


FIG.  8-1, 


where  a  normal  combustion  mixture 
is  formed  by  the  addition  of  more 
air.  The  jacket  water  from  the  engine 
may  be  circulated  through  /,  assisting 
in  the  vaporization.  In  special  cases 
a  part  of  the  exhaust  gases  may  also 
^  be  circulated  through  the  bottom,  g. 

Figures  8-2  and  8-3  are  properly 
termed  surface  carbureters.  In  the 
former,  the  Reithman  carbureter,  the 
gasoline  is  fed  from  the  reservoir  a  in 
drops  into  the  chamber  b,  where  it  is 
absorbed  by  broad  suspended  wicks. 
From  the  surfaces  of  these  the  gaso- 
line vaporizes,  adding  itself  to  the 
air  which  strikes  through  chamber 
b  on  every  suction  stroke.  Chamber 
/  is  filled  with  clean  gravel  or  wire 


FIG.  8-2  —  Reithman  Carbureter. 

screens,  to  act  as  a  safety  device  against  possible  back  firing. 
Chamber  b  is  surrounded  by  a  water  jacket,  the  water  in 
which  is  heated  by  the  exhaust  gases  passing  through  the 
tubes  d  d. 


GAS-ENGINE  FUELS 


187 


The  Petreano  carbureter,  Fig.  8-3,  will  serve  for  either  gasoline 
or  alcohol.  The  exhaust  gases  pass  through  a  central  pipe,  r, 
which  is  surrounded  by  a  jacket,  V.  The  pipe  r  has  a  covering, 
d,  of  spongy  asbestos  film  which  is  constantly  kept  moist  with 
the  liquid  to  be  vaporized.  The 
liquid  fuel  enters  by  one  open- 
ing in  the  top,  the  air  by  an- 
other. The  chamber  V  has  four 
cones,  as  shown,  two  of  which 
are  also  partially  covered  with 
asbestos.  By  means  of  these 
cones  the  fuel  vapor  and  air  are 
thoroughly  mixed  before  enter- 
ing the  chamber  M  and  finally 
the  suction  pipe  to  the  engine. 
The  small  openings,  o,  are  for 
the  purpose  of  drawing  off  the 
heavier  parts  of  the  liquid,  those 
that  vaporize  less  easily,  if  there 
be  any,  in  order  not  to  interfere 
with  the  regularity  of  carbureting.  FlG-  *-3-  —  Petreano  Carbureter. 

Atomizing  or  spraying  carbureters  are,  however,  much  more 
frequently  employed,  and  the  following  to  be  described  are  .all  of 
this  type. 

1  e 


Semi -Sectional 

SECTION  ON  A-B.          'Views. 


SECTION  OMA-t. 


Angle  Pattern.  Vertical  Pattern. 

FIG.  8-4.  —  Lunkenheimer  Mixing  Valves. 


188 


INTERNAL  COMBUSTION  ENGINES 


The  simplest  design  of  this  type  of  carbureter  is  shown  in 
Fig.  8-4,  which  shows  two  of  the  Lunkenheimer  carbureters.  In 
either  design,  gasoline  is  furnished  through  the  opening  0,  and 
its  admission  to  the  valve  seat  of  the  main  suction  valve  E  is 
regulated  by  the  needle  valve  A.  On  the  suction  stroke  of  the 
engine  the  valve  E  automatically  lifts,  and  the  air  rushing  through 
this  opening  carries  with  it  a  certain  amount  of  gasoline  flowing 
from  the  small  hole  K.  It  is  quite  evident  that  this  type  of  car- 
bureter gives  best  service  on  hit-and-miss  engines.  For  any 
other  type  a  varying  load  would  probably  cause  trouble,  as  there 
is  no  automatic  regulation  of  the  gasoline  supply. 

Still  of  very  simple  design,  but 
capable  of  regulation  of  the  gasoline 
supply,  is  the  Sintz  carbureter,  Fig. 
8-5.  The  lift  of  the  gasoline  needle 
valve  b  is  regulated  by  the  lift  of 
the  mechanically  regulated  suction 
valve  a.  By  means  of  the  cock  c  it 
is  possible  to  admit  part  of  the  air 
uncarbureted  to  the  cylinder. 

Figures  8-6  and  8-7  are  examples 
of  the  so-called  float-feed  type  of 
carbureters. 

The  Daimler,  Fig.  8-6,  is  well 
FIG.  8-5.  — Sintz  Carbureter,  known.  A  float,  B,  in  the  cham- 
ber, A,  operates  a  pair  of  counterweight  levers,  E,  and  through 
them  the  valve  spindle,  D,  which  controls  the  admission  of 
gasoline  at  C,  keeping  it  at  a  constant  level  in  the  nozzle.  Gaso- 
line enters  at  N  from  a  tank  under  slight  pressure  or  at  a  higher 
level.  0  is  a  cloth  filter  and  the  plug  P  serves  to  catch  any  grit 
that  may  be  brought  in.  The  float  chamber  is  vented  through  a 
small  hole  in  the  cap  over  the  valve  spindle  to  relieve  any  pres- 
sure which  may  be  formed  due  to  varying  positions  of  the  float  B. 
The  action  of  the  carbureter  is  as  follows:  At  each  charging 
stroke  of  the  engine  air  is  drawn  into  the  annular  chamber  H 
and  passes  with  great  velocity  through  the  drop  tube  F,  surround- 
ing the  gasoline  nozzle.  The  gasoline  is  drawn  in  a  jet  from  the 
nozzle  and,  with  the  air,  striking  the  deflector  K,  the  two  are  very 
thoroughly  mixed,  passing  to  the  engine  through  M.  An  aux- 


GAS-ENGINE  FUELS 


189 


iliary  air  supply  can  be  admitted  through  the  cap  at  the  top,  the 
openings  through  which  can  be  regulated. 


FIG.  8-6.  —  Daimler  Carbureter. 


FIG.  8-7.  —  Abeille  Carbureter. 

The  Abeille  carbureter,  Fig.  8-7,  embodies  the  same  idea  as 
the  Daimler.  The  float  B,  by  operating  the  lever  D,  opens  and 
closes  a  needle  valve  at  the  lower  end  of  the -weighted  spindle  C, 
to  maintain  a  constant  level  just  below  the  opening  in  the  nozzle 


190 


INTERNAL  COMBUSTION  ENGINES 


E.  On  the  suction  stroke,  air  enters  at  H,  and  rushing  up  through 
the  double  cone  draws  the  gasoline  from  the  nozzle,  atomizing  it 
by  striking  the  perforated  cone  G.  A  secondary  air  supply  is 
admitted  through  the  cap  L  and  the  holes  in  G,  being  regulated 
by  the  position  of  the  cap  L. 


FIG.  8-8.  — De  Dion  Carbureter. 

Of  more  complicated  design,  but  in  principle  the  same  as  the 
other  float-feed  carbureters,  is  the  De  Dion,  Fig.  8-8.  Air  is 
admitted  through  the  tube  t.  By  the  position  of  the  valve  V  (see 
horizontal  section),  which  position  can  be  regulated  by  the  lever/ 
(see  vertical  section),  part  of  the  air  goes  directly  into  the  dis- 
charge pipe  t' ',  while  the  rest  is  deflected  downward  to  be  car- 
bureted. The  course  of  this  latter  body  of  air  is  indicated  in  the 
right  vertical  section  by  the  arrow.  The  level  of  the  gasoline  in 
the  nozzle  D  is  again  kept  constant  by  the  annular  float  C  in  the 
chamber  H,  operating  the  lever  G  and  through  it  the  valve  F. 

It  will  be  noted  that  none  of  the  atomizing  or  spraying  carbu- 
reters for  gasoline  so  far  described  are  heated  in  any  manner. 
Occasionally,  however,  we  find  one  in  which  the  atomizing  is 
assisted  by  heat.  The  W.  Hay  vaporizer,  Fig.  8-9,  is  of  this 
type.  Gasoline  enters  the  annular  chamber,  a  a,  through  the 
pipe  d.  From  this  chamber  a  number  of  small  openings  lead 
through  the  seat  of  the  suction  valve  E.  Some  of  these  openings 
are  provided  with  adjusting  screws  as  shown  at  the  left.  On 


GAS-ENGINE  FUELS 


191 


the  opening  of  E,  the  inrush  of  air  atomizes  the  gasoline  flow- 
ing from  these  small  openings,  and  the  current  of  air  and  gaso- 
line striking  the  wings  e  of  the 
fan  h,  supported  on  the  spindle 
/,  sets  the  fan  in  motion,  thus 
promoting  a  thorough  mixture  of 
air  and  vapor  before  the  fuel 
finally  passes  through  x  to  the 
admission  valve  A.  The  ex- 
haust gases  from  B  are  passed 
through  the  chamber  F,  finally 
escaping  through  the  slotted 
openings  '  g.  In  their  passage 
they  heat  both  the  gasoline 
storage  chamber  a  a  and  the 
fan  chamber. 

Occasionally    we     also     find 
carbureters  which  combine   the 
several   principles    of   those    de-      FIG.  8-9.  —  W.  Hay  Vaporizer, 
scribed.     Thus  in  the  Gautier  carbureter,  Fig.  8-10,  the  gasoline 
is  admitted  through  A,  the  supply  being  regulated  by  the  valve 


FIG.  &-10.  —  Gautier  Carbureter. 

K,  which  opens  at  the  proper  moment  owing  to  suction  through 
pipe  E.  Part  of  the  supply  falls  on  to  the  saucer  F,  and  from 
there  into  the  reservoir  H.  Into  the  liquid  at  H  dips  a  pipe  Gr 


192  INTERNAL  COMBUSTION  ENGINES 

supported  as  shown.  The  air  supply  through  /  circulates  through 
the  chamber  L,  bubbles  through  the  liquid  at  H  into  the  chamber 
surrounding  the  saucer  F,  licks  up  some  of  the  gasoline  in  the 
saucer,  and  the  mixture  finally  escapes  through  E. 

VAPORIZING  DEVICES  FOR  CRUDE  OIL  AND  KEROSENE.  — 
While  it  is  fairly  easy  to  satisfactorily  atomize  or  vaporize 
gasoline  and  to  maintain  the  mixture,  the  thing  is  a  little  more 
difficult  with  kerosene,  and  much  more  so  with  crude  oil.  In 
either  case  the  agency  of  heat  is  required,  and  this  is  applied 
either  in  a  separate  vaporizer  or  retort,  or  the  kerosene  or  crude 
oil  is  injected  directly  into  the  cylinder,  the  vaporization  taking 
place  in  the  combustion  chamber. 

One  trouble  with  kerosene  is  the  readiness  with  which  some 
of  the  vapor  is  condensed  on  striking  comparatively  cool  sur- 
faces. This  may  happen  on  the  mixture  striking  parts  of  the 
water-cooled  walls.  In  such  a  case  part  of  the  fuel  may  go  through 
the  cylinder  unburned,  and  this  is  a  point  that  should  be  care- 
fully guarded  against  when  a  special  vaporizer  for  kerosene  is 
employed. 

In  the  case  of  crude  oil,  the  heating  in  the  vaporizer  results 
in  the  distillation  of  the  lighter  products  first.  The  amount  of 
vapor  formed  will  naturally  be  less  and  less  as  the  distillation 
proceeds,  resulting  in  a  constant  impoverishing  of  the  fuel  mix- 
ture. The  remedy  would  therefdre  seem  to  be  a  constant  supply 
of  fresh  oil  and  a  removal  of  the  old  before  it  has  commenced 
to  seriously  decrease  its  yield.  This  is  what  is  actually  done 
in  some  devices.  The  method,  however,  naturally  results  in  the 
fact  that  the  plant  can  only  use  part  of  the  crude  oil.  It  is 
claimed  by  some  that  only  10  per  cent  of  the  oil  is  so  withdrawn 
from  the  vaporizer,  but  this  seems  extremely  doubtful. 

A  crude  oil-air  mixture  is  open  to  the  same  objection  as  a 
kerosene  mixture  as  regards  condensation  of  some  of  the  heavier 
hydrocarbons  and  consequent  loss.  Both  of  these  mixtures  are 
also  subject  to  cracking;  that  is,  a  breaking  up  of  the  heavier 
hydrocarbons  into  the  lighter  with  a  consequent  deposit  of  carbon. 

For  large  power  plants  the  best  solution  in  the  case  of  crude 
oil  would  seem  to  be  the  use  of  some  type  of  oil-gas  producer. 
Some  of  these  are  in  actual  use  along  the  Pacific  coast,  and  will 
be  described  later. 


GAS-ENGINE  FUELS 


193 


Figure  8-11  shows  the  kerosene  atomizer  used  on  the  Hornsby 
engine.  With  it  is  combined  the  regulating  valve.  Kerosene 
is  pumped  up  through  the  lower  right-hand  pipe  in  the  sectional 
cut.  The  governor  regulates  through  c  the  position  of  the  over- 
flow valve  bj  the  surplus  kerosene  flowing  back  through  d  to  the 
reservoir.  The  kerosene  at  the  moment  demanded  by  the  engine 


FIG.  8-11.  —  Hornsby- Akroyd  Atomizer. 

is  forced  by  the  pump  through  the  plug  a,  issuing  from  its  end  in 
a  fine  spray.     This  plug  is  kept  cool  by  a  water  jacket  as  shown. 

Another  atomizing  kerosene  carbureter  is 
the  Gibbon,  shown  in  Fig.  8-12.  In  this  a 
valveless  pump  x  w,  actuated  by  a  cam, 
injects  kerosene  from  the  tank  up  through 
the  atomizing  opening  into  the  chamber  U. 
This  is  furnished  with  wings,  U',  to  pre- 
sent a  larger  surface  for  heating.  Chamber  U 
is  directly  connected  with  the  combustion 
chamber,  and  is  surrounded  by  a  light  case 
to  prevent  radiation.  At  the  start  it  is 
heated  by  a  lamp,  but  after  a  short  period 
of  operation  the  charge  ignites  by  compres- 
sion, as  is  the  case  also  in  the  Hornsby 
engines. 

In  the  Crossley  vaporizer,  Fig.  8-13,  a 
certain  fixed  amount  of  oil  is  measured  and 

drawn  into  the  vaporizer  by  the  air  on  the 

.  .?.  .      ...        FIG.  8-12.  —  Gibbon 

opening  of  the  valve.     In  this  case  ignition   Kerosene  Vaporizer. 


194 


INTERNAL  COMBUSTION   ENGINES 


is  produced  by  means  of  a  hot  tube,  and  the  engine  is  of  course 
governed  on  the  hit-and-miss  system.  The  lamp  heating  the  hot 
tube  at  the  same  time  heats  the  vaporizer. 


FIG.  8-13.  —  Crossley  Vaporizer. 

The  Priestman  engine  is  designed  for  either  crude  oil  or  kero- 
sene. Its  vaporizer  is  shown  in  Figs.  8-14  and  8-15.  Oil  is  ad- 
mitted to  the  spraying  nozzle  K  from  a  reservoir  under  pressure. 


EXHAUST 

FIG.  8-14.  —  Priestman  Vaporizer. 


Petrofeum 


FIG.  8-15.  —  Priestman  Vaporizer. 


GAS-ENGINE  FUELS 


195 


The  pump  furnishing  the  air  for  this  purpose  also  furnishes  air  to 
the  annular  space  J ,  surrounding  the  nozzle  K,  for  the  purpose 
of  atomizing  the  oiK  The  finely  divided  oil  enters  the  vaporizer 
chamber  and,  mixing  with  the  larger  body  of  air  admitted  on 
the  suction  stroke  to  the  vaporizer  chamber  through  the  valve  L, 
passes  on  to  the  cylinder.  The  vaporizer  chamber,  Fig.  8-15,  is 
heated  by  the  exhaust  gases  passing  through  the  jacket  space  C, 
thus  vaporizing  the  oil  spray  in  its  passage.  On  starting,  the 
vaporizer  chamber  is  heated  by  a  lamp  whose  hot  gases  pass 
through  the  jacket  spaces  d.  The  governor,  by  regulating  the 
position  of  the  plug  valve  H ,  regulates  at  the  same  time  both  the 
oil  and  the  air  supply  to  the  vaporizer. 

A  crude  oil  vaporizer  quite  extensively  used  on  the  Pacific 
coast  is  the  " Economist"  retort,  Fig.  8-16.     This  consists  of 


FIG.  8-16.  —  "  Economist"  Crude  Oil  Vaporizer. 

two  concentric  shells  as  shown.  In  the  jacket  space  between 
them  the  engine  exhaust  gases  are  circulated  to  furnish  the  heat 
for  vaporization.  The  inner  drum  is  slowly  rotated  upon  its  axis, 
as  shown  by  the  gearing  at  the  right,  and  it  is  furnished  on  the 
interior  with  a  continuous  spiral  rib.  The  crude  oil  is  admitted 
through  the  central  pipe  at  the  left.  By  the  rotation  of  the 
drum  it  is  carried  up  the  sides,  turned  over  and  over,  thus 
exposing  a  thin  sheet  all  the  time  to  the  action  of  the  heat, 
which  is  most  favorable  for  complete  vaporization.  At  the  same 
time,  owing  to  the  action  of  the  spiral  rib,  the  oil  is  slowly  carried 
forward  through  the  drum.  The  residue  is  finally  discharged 
through  an  outlet  at  the  right,  in  a  manner  not  clearly  shown. 
The  makers  claim  that  during  the  progress  of  the  oil  through 
the  drum  the  temperature  is  maintained  just  high  enough  to 
get  all  the  gas  from  the  oil.  The  method  of  regulation  by  this 
device  is  not  clearly  stated.  If  it  is  done  by  regulating  the  oil 


196  INTERNAL  COMBUSTION  ENGINES 

supply  to  the  retort  according  to  the  load,  there  would  be  con- 
siderable lag  in  the  regulation;  if  done  by  regulating  the  air 
supply  through  the  retort  there  would  be  a  large  variation  in 
the  composition  of  the  mixture.  An  auxiliary  air  supply  between 
generator  and  engine  would  help,  but  whether  this  is  used  or  not 
is  not  stated. 

Retorts  as  above  described  are  made  up  to  from  125  to  150 
horse-power.  Beyond  this  they  become  unsatisfactory,  and 
other  devices  have  to  be  employed.  The  one  that  seems  to 
promise  best  at  present  is  an  oil-gas  generator  of  the  type  of  the 
Lowe. 

The  principle  of  the  Lowe  system  is  to  heat  up  to  a  very  high 
temperature  a  mass  of  firebrick  checker  work  contained  in  a  fire- 
brick-lined steel  shell,  by  means  of  a  crude  oil-air  blast.  When 
the  desired  temperature  is  reached  the  chimney  connection  to 
the  generator  is  closed  off,  and  crude  oil  and  superheated  steam 
in  an  intimate  mixture  are  sent  down  through  the  highly  heated 
checker  work.  The  result  is  the  formation  of  an  impure  oil 
water  gas  with  a  good  deal  of  lampblack  as  a  by-product.  This 
by-product  may  be  utilized  as  fuel  to  furnish  the  power  necessary 
for  blowing  engines,  etc.,  around  the  plant.  The  gas  itself  is 
washed  in  the  ordinary  manner,  and  is  a  high-grade  gas  of  good 
illuminating  power.  The  production  of  this  gas  is  therefore 
carried  on  in  the  two  stages,  a  heating-up  period  and  a  period  of 
make.  From  published  figures  the  efficiency  of  these  oil-gas  pro- 
ducers is  as  yet  not  very  high.  In  the  Journal  of  Electricity, 
Power  and  Gas,  September,  1904,  a  consumption  of  11.22  gallons 
of  oil  per  1000  cubic  feet  of  gas  made  is  given  as  the  average 
for  one  plant  for  July.  Other  plants  have  shown  9  and  10  gal- 
lons per  1000  cubic  feet  of  gas  of  about  the  same  heating  value. 
Assuming  the  crude  oil  to  weigh  7  pounds  per  gallon,  its  heating 
value  at  19000  B.  T.  U.  per  pound,  and  the  heating  value  of  the 
gas  at  650  B.  T.  U.  per  cubic  foot,  the  efficiency  of  generation 
on  cold  gas  would  be  for  the  most  favorable  case  above  given 

1000X650    .= 


9X7X19000 

VAPORIZING    DEVICES    FOR   ALCOHOL.  —  The   alcohol    engine 
has   perhaps   received   its   greatest    development    in    Germany. 


GAS-ENGINE  FUELS  197 

It  is  for  that  reason  that  we  shall  have  to  turn  to  the  literature  of 
that  country  for  the  best  and  latest  information  on  the  details 
of  alcohol  engines. 

The  following  material  is  a  reprint  from  an  article  published 
by  the  writer  on  the  alcohol  question  in  Marine  Engineering, 
June,  1906.  The  information  is  mainly  due  to  the  work  of  E. 
Meyer  and  of  A.  Schottler,  also  to  the  discussions  by  Giildner, 
Diesel,  and  others.  * 

Regarding  the  formation  of  the  fuel  mixture  with  alcohol,  it 
is  found  that  it  is  less  volatile  than  gasoline,  but  easier  to  handle 
than  kerosene.  In  nearly  all  of  the  vaporizing  devices  for  alcohol 
now  on  the  market,  the  agency  of  heat,  usually  the  exhaust  heat 
of  the  waste  gases,  is  used  to  aid  in  the  formation  of  the  mixture. 
This  scheme  has  the  drawback  that  no  heat  is  available  at  the  start 
when  the  engine  is  cold.  To  avoid  an  open  flame  for  the  purpose 
of  heating  the  vaporizer  at  the  start,  which  is  both  dangerous 
and  cumbersome,  the  engines  in  most  cases  are  started  with  gaso- 
line, and  when,  after  a  few  strokes,  enough  heat  is  available,  the 
change  is  usually  made  by  throwing  over  a  single  lever.  In 
tests  of  ten  different  engines  made  by  Meyer,  it  was  shown  that 
this  change  to  alcohol  could  be  made  in  the  slowest  case  in  6 
minutes  and  40  seconds,  the  time  of  the  fastest  being  55  seconds. 

Based  on  the  manner  of  heating  the  vaporizer,  we  can  dis- 
tinguish the  following  classes: 

1.  Those  in  which  no  heat  is  employed. 

2.  Those  in  which  the  air  is  pre-heated. 

3.  Those  in  which  the  mixture  is  heated  and  superheated. 
Of  the  first  type  is  the  Deutz,  Figs.  8-17  and  8-18.     When  the 

engine  is  regulated  by  the  throttling  method,  and  not  by  the 
hit-and-miss  system,  it  has  been  found  that  no  pre-heating  of 
air  or  fuel  mixture  is  required.  The  reason  for  this  is  un- 
doubtedly that  in  a  hit-and-miss  engine,  under  less  than  normal 
load,  a  succession  of  misses  cools  the  cylinder  down  so  far  as  to 
throw  down  some  of  the  alcohol  vapor  on  the  next  explosion, 
unless  it  is  superheated.  The  Deutz  engine  is  governed  by 
throttling.  The  inlet  valve  /  is  actuated,  through  the  levers 

*  E.  Meyer,  Zeitschrift  d.  V.  d.  I.,  1903,  pages,  513,  600,  632,  669;  R. 
Schottler,  Zeitschrift  d.  V.  d.  I.,  1902,  pages,  1157,  1223;  H.  Giildner,  Zeit- 
schrift d.  V.  d.  I.,  1902,  page  623;  Diesel,  Zeitschrift  d.  V.  d.  I.,  1903,  page 
1366. 


198 


INTERNAL  COMBUSTION  ENGINES 


shown,  by  the  cam   a,  which  is  of  taper  form  and  under  the 
control  of    the   governor   Fig.  8-17.     Upon   the   position  of    a 

depends  the  length  of  time  the  valve 
/  is  open.  Through  the  bell  crank 
c  d  e  the  cam  also  acts  upon  the 
plunger  of  the  fuel  pump  h,  operat- 
ing in  such  a  way  as  to  cause  suction 
during  the  first  part  of  the  cam 
movement,  and  pumping  of  the 
liquid  during  the  second.  Thus  the 
fuel  is  injected  during  the  second 
FlG>  8_]  7.  _  Deutz  Alcohol  half  of  the  suction  stroke  only,  insur- 
Vaporizer.  ing  a  rich  mixture  around  the  igniter. 

The  alcohol  is  forced  through  the  sprayer  or  atomizer  i, 
Fig.  8-18,  into  the  current  of  air  which  enters  through  the 
valve  k.  Thus  no  pre-heating  what- 
ever is  done,  but  the  atomizing  is 
thorough;  and  the  ports  into  the 
cylinder  are  as  direct  and  short  as 
possible,  hence  no  vapor  is  thrown 
down. 

The  Altman  vaporizer,  Fig.  8-19, 
is  of  the  second  class.  The  air  pipe 
a — b  is  surrounded  at  its  lower  end 
by  the  exhaust  pipe;  the  air  is  thus 
pre-heated  by  the  exhaust  gases. 
A  regulating  valve  for  the  air  is 
placed  at  e.  This,  when  drawn  up- 
ward, decreases  the  amount  of  air 
passing,  but  always  makes  the  air 
current  strike  through  the  upper  part 
of  the  pipe,  in  this  manner  directing 
it  always  against  the  fuel  nozzle  d.  The  inlet  valve  c  is 
operated  by  the  lever  /,  actuated  by  the  cam  /,  through  the 
pendulum  hit-and-miss  governor  o  m  p.  This  valve  lever  /  at  the 
same  time  opens  the  fuel  valve  d,  through  the  reach  rod  shown  and 
the  finger  h  i,  Fig.  8-21.  How  this  is  done  is  shown  in  Fig.  8-20. 
The  lever  /,  on  being  depressed,  forces  down  the  point  of  the  screw 
k,  thereby  turning  the  reach  rod  about  its  axis,  which  depresses 


FIG. 


8-18.—  Deutz  Alcohol 
Vaporizer. 


GAS-ENGINE  FUELS 


the  point  i,  Fig.  8-21 ,  opening  the  valve  d.  The  amount  of  opening 
depends  upon  the  position  of  the  screw  k,  and  this  can  be  very 
finely  adjusted  by  the  worm  and  wheel  arrangement  shown.  In 
this  vaporizer  the  fuel  supply  is  atomized  partly  by  the  current  of 
ir;  and  is  afterwards  vaporized  by  the  heat  of  the  pre-heated  air. 


FIG.  8-19.  —  Altman  Alcohol  Vaporizer. 


FIG.  8-20. 


FIG.  8-21. 


The  following  three  vaporizers  are  of  the  third  class.  Fig.  8-22 
shows  the  Swiderski-Longuemarre.  Here  also  the  exhaust  gases 
are  used  for  heating.  They  pass  through  the  annular  chamber  a, 
and  their  action  is  aided  by  the  radiating  webs  b  b.  The  float  d 
maintains  a  constant  level  in  the  supply  chamber.  From  this 
chamber  the  flow  of  alcohol  is  regulated  by  the  needle  valve  /. 


200 


INTERNAL  COMBUSTION  ENGINES 


The  liquid  flows  into  the  space  g,  and  overflows  through  a  num- 
ber of  small  openings  h  h.  Air  entering  through  i  is  made  to 
pass  partly  outside,  partly  inside,  the  concentric  spaces  created 


FIG.  8-22.  —  Swiderski-Longuemarre  Alcohol  Carbureter. 


FIG.  8-23.  —  Dresden  Alcohol 
Vaporizer. 


FIG.  8-24.  — Dresden  Alcohol 
Vaporizer. 


GAS-ENGINE  FUELS 


201 


by  the  sleeve  k.  The  amount  of  air  passing  outside  is  regulated 
by  the  openings  n  n  which  are  controlled  by  the  lever  I.  The  air 
currents  passing  upward  carry  along  with  them  some  of  the  liquid, 
the  mixture  being  heated  by  the  exhaust  gases  in  a.  The  per- 
,.  forated  plate  o  tends  to  aid  in  forming  a  uniform  mixture. 

The  vaporizer  of  the  Dresdener  Gasmotorenfabrik  is  shown  in 
Figs.  8-23  and  8-24.  In  this  case  the  warm  cooling  water  of  the 
engine  is  used  for  heating.  It  enters  the  water  space  at  x,  Fig. 
8-24.  On  very  cold  days  the  vaporization  may  be  assisted  at 
the  start  by  pouring  some  hot  water  into  the  funnel  a.  Air  enters 
at  y,  8-23.  The  inlet  valve  b  is  automatic.  It  may  be  pushed 
down  at  will  at  the  start  by  pressing  down  on  the  projecting  stem 
c.  The  downward  movement  of  the  inlet  wave  opens  the  fuel 
valve  d,  to  which  alcohol  is  furnished  through  the  needle  valve 
e,  Fig.  8-24.  Through  a  number  of  fine  openings  the  fuel  flows 
into  the  current  of  air  and  is  carried  along  with  it,  the  thorough 
mixing  being  assisted  by  the  current 
striking  the  cone  g.  As  will  be  seen 
from  the  drawing,  the  heating  of  the 
charge  cannot  be  very  high.  In  the 
first  place  only  the  comparatively  cool 
jacket  water  of  the  engine  is  used, 
and  secondly  the  mixture  itself  is  not 
in  the  heated  chamber  for  any  length, 
of  time. 

In  contradistinction  to  the  Dresden 
vaporizer,  the  Diirr,  Fig.  8-25,  pro- 
duces a  highly  heated  mixture.  Air 
enters  at  x  and  its  amount  is  regu- 
lated by  the  throttle  valve  a.  The 
inlet  valve  b  is  automatic.  Alcohol 
is  supplied  through  the  needle  valve 
c,  as  shown,  so  that  when  b  is  closed 
no  flow  of  alcohol  takes  place.  The 
current  of  air  charged  with  alcohol 
particles  passes  down  through  d,  up 
the  annular  space  e,  and  out  at  y  to 
the  cylinder.  The  exhaust  gases  enter 


at  z,  and  by  means  of  baffle   plates 


FIG.  8-25.  —  Diirr  Alcohol 
Vaporizer. 


202 


INTERNAL  COMBUSTION  ENGINES 


are  made  to  take  the  course  shown  by  the  arrows,  through  the  space 
/.  Further,  the  space  e  is  filled  with  a  large  number  of  metal 
spirals,  which  connect  the  outside  wall  of  e  with  its  inside  wall, 
thus  furnishing  a  large  heated  surface  to  the  passage  of  the  charge, 
and  facilitating  the  transfer  of  heat  from  the  space  /  to  the 
space  d.  Every  possible  way  is  therefore  made  use  of  to  apply 
the  heat  of  the  exhaust  gases,  and  this  vaporizer  consequently  fur- 
nishes a  mixture  more  highly  superheated  than  that  of  the 
others. 


FIG.  8-26.  —  Gasoline-Alcohol  Vaporizer. 

Finally,  Fig.  8-26  shows  what  may  be  called  a  double  float 
carbureter,  which  is  the  form  that  alcohol  vaporizers  are  likely 
to  take.  This  is  used  on  the  Marienfelde  machines.  Assume 
that  the  chamber  a  is  used  for  gasoline,  b  for  alcohol.  The  needle 
supply  valves  can  be  held  closed  by  the  springs  c  and  d,  as  shown. 

On  starting  with  gasoline,  the  chamber  a  is  used.  Spring  c 
is  pushed  aside  so  that  fuel  can  enter,  being  kept  at  constant 
level  by  the  float.  The  valve  g  is  so  set  that  the  path  is  open  for 
the  air  from  h  past  the  gasoline  nozzle  e,  through  g  into  the 
cylinder.  At  every  suction  stroke  the  in-rushing  air  is  then 
charged  with  gasoline  issuing  in  a  small  jet  from  e.  If  it  is  de- 
sired to  change  to  alcohol,  spring  c  is  pushed  into  place,  spring  d 


GAS-ENGINE  FUELS  203 

is  pushed  aside,  and  valve  g  is  thrown  over  into  the  position 
shown  in  Fig.  10,  all  the  work  of  a  moment.  The  air  supply  to 
this  vaporizer  is  pre-heated. 

It  is  quite  evident  from  an  examination  of  the  vaporizers  above 
described  that  the  final  temperature  of  the  mixture  is  very  differ- 
ent in  the  different  devices.  Upon  this  temperature,  however,  de- 
pends in  a  great  measure  the  only  other  point  of  difference  between 
gasoline  and  alcohol  engines,  i.e.,  the  amount  of  compression. 
All  other  things  being  the  same,  that  fuel  mixture  entering  the 
cylinder  at  the  highest  temperature  will  soonest  give  rise  to  pre- 
ignition,  or  at  least  to  pounding,  under  an  increase  in  compression. 
High  temperature  of  charge  also  effects  engine  capacity  unfavor- 
ably. It  therefore  becomes  important  to  determine  approxi- 
mately the  lowest  practical  temperature  of  vaporization,  and  the 
heat  necessary. 

Of  course  the  amount  of  heat  required  depends  upon  the 
amount  of  alcohol  (and  its  purity)  per  pound  or  cubic  foot  of 
air.  Assuming  that  90  volume-per  cent  alcohol  is  used,  the 
theoretical  amount  of  air  required  for  perfect  combustion  is  7.8 
pounds.  Assuming  that  an  excess  of  50  per  cent  of  air  is  used, 
which  is  a  desirable  allowance,  1  pound  of  90  per  cent  alcohol 
would  require  in  round  numbers  11.7  pounds  of  air.  With  the 
air  temperature  at  60  degrees  Fahrenheit,  and  the  atmospheric 
pressure  14.7  pounds  per  square  inch,  this  amounts  to  0.0065 
pound  of  90  per  cent  alcohol  per  cubic  foot  of  dry  air. 

90  (volume)  per  cent  alcohol  is  equivalent  to  87.7  (weight) 
per  cent,  so  that  1  pound  of  air  will  carry,  according  to  the  above 
assumed  ratio  of  mixture, 

0.877  X  j-j-s  =  0.075  pound  of  absolute  alcohol, 

and  0.123  X  ^  =  0.010  pound  of  water. 

To  compute  the  air  temperature  required  so  that  it  may  take 
up  the  above  quantities  of  alcohol  and  water  vapor,  we  must 
know  the  relation  between  the  temperature  and  the  degree 
of  saturation.  Meyer  in  his  computations  used  the  data 
contained  in  the  Physikalisch-Chemische  Tabellen  of  Landoldt  & 
Bornstein. 


204 


INTERNAL  COMBUSTION  ENGINES 


Temperature 
Degrees  F 

Vapor  Tension 
Inches  Mercury 

1  pound  of  air  contains  in  saturated 
condition,  in  pounds 

Alcohol 
Vapor 

Water 
Vapor 

At  28.95  inches 
Hg.  Press. 

At  26.05  inches 
Hg.  Press. 

Alcohol 
Vapor 

Water 
Vapor 

Alcohol 
Vapor 

Water 
Vapor 

50 

0.950 

0.359 

0.055 

0.008 

0.061 

0.009 

59 

1.283 

0.500 

0.075 

0.011 

0.084 

0.013 

68 

1.733 

0.687 

0.104 

0.016 

0.117 

0.018 

77 

2.325 

0.925 

0.144 

0.022 

0.162 

0.025 

86 

3.090 

1.240 

0.200 

0.031 

0.227 

0.036 

104 

5.270 

2.162 

0.390 

0.063 

0.450 

0.072 

122 

8.660 

3.620 

0.827 

0.135 

1.002 

0.164 

For  our  purpose  the  figures  of  the  table  have  been  transposed 
into  English  units. 

In  the  ordinary  case  the  air  drawn  into  the  vaporizer  is  not 
dry,  but  contains  a  certain  quantity  of  water.  Assume  that  the 
air  is  at  a  temperature  of  59  degrees  and  just  saturated.  At  a 
pressure  of  26.05  inches  of  mercury  this  would  correspond  to 
0.013  pound  of  water  per  pound  of,  air  in  its  initial  condition. 
Now  in  the  case  of  the  average  mixture  above  computed,  the  tem- 
perature of  vaporization  must  be  high  enough  to  vaporize  an 
additional  0.010  pound  of  water,  making  the  total  0.023  pound 
that  the  air  must  contain  per  pound.  It  is  seen  from  the  table 
that  a  temperature  of  77  degrees  is  quite  sufficient  to  do  this. 
It  is  also  seen  that  at  this  temperature  the  air  may  take  up  0.162 
pound  of  absolute  alcohol,  while  the  quantity  in  the  above  mixture 
is  only  0.075  pound  per  pound  of  mixture.  At  a  tempera- 
ture of  77  degrees  the  mixture  ready  for  the  cylinder  may  there- 
fore contain  the  alcohol  vapor  in  a  state  of  some  superheat.  If 
therefore  the  temperature  of  the  walls  with  which  the  mixture 
comes  in  contact  is  not  less  than  77  degrees,  no  fear  of  condensa- 
tion of  alcohol  vapor  need  be  entertained.  In  this  connection 
a  statement  in  the  Engineering  Record  is  of  interest.  It  is  there 
claimed  that  the  consumption  of  alcohol  with  the  jacket  water 
leaving  at  60  degrees  Fahrenheit  is  100  per  cent  higher  than  with 
jacket  water  leaving  near  212  degrees;  i.e.,  with  cooling  by 


GAS-ENGINE  FUELS  205 

vaporization.  In  the  light  of  the  above  facts,  some  such  increase 
in  the  consumption  is  quite  possible. 

In  order  to  convert  the  liquid  alcohol  into  vapor,  a  certain 
quantity  of  heat  is  required.  According  to  Regnault,  this  amount 
is,  for  the  various  temperatures  given,  and  computed  above  32 
degrees  Fahrenheit,  as  follows: 

At  32°  F  425.7  B.  T.  U.  per  pound 

68°  F  453.6  B.  T.  U.  per  pound 

122°  F  475.2  B.  T.  U.  per  pound 

212°  F  481.1  B.  T.  U.  per  pound 

The  specific  heat  of  liquid  alcohol  is  close  to  0.6,  so  that  in 
order  to  convert  the  quantity  of  90  volume-per  cent  alcohol  con- 
tained in  the  assumed  mixture  to  alcohol  vapor  at  77  degrees 
Fahrenheit  would  require  approximately,  assuming  the  liquid 
alcohol  at  60  degrees  Fahrenheit,  0.075  X  [458  -  (28  X  0.6)]  + 
[0.010  X  1100]  =  44.1  B.  T.  U.,  where  1100  B.  T.  U.  is  assumed 
as  the  heat  of  vaporization  of  water  under  the  existing  conditions. 

Now  the  heating  value  of  90  volume-per  cent  alcohol  has  been 
shown  to  be  10080  B.  T.  U.  per  pound,  so  that  the  heating  value 
on  one  pound  of  our  assumed  mixture  will  be  0.075  X  10080  = 

44  1 

756  B.  T.  U.     The  heat  of  vaporization  required  is  therefore  — ^~ 

756 

=  5.8  per  cent  of  the  heating  value  of  the  fuel.  It  can  be  shown 
that  the  amount  of  heat  is  easily  obtainable  from  the  exhaust 
gases.  It  can  also  be  shown  that  the  problem  may  be  solved  by 
pre-heating  the  air  only,  for,  assuming  that  the  specific  heat  of 
air  at  constant  pressure  is  0.238,  we  would  have  to  pre-heat  the 

44.1 

air  for  the  assumed  mixture  to  — ~   +  77  ••=  262  degrees  Fahren- 

.Zoo 

rieit,  which  is  easily  possible. 

If,  on  the  other  hand,  not  the  air  but  the  mixture  is  heated, 
then  the  walls  need  to  have  a  temperature  only  sufficiently  higher 
than  77  degrees  to  transfer  the  required  amount  of  heat  for  vapori- 
zation to  the  mixture  in  the  time  available.  To  furnish  more 
heat  than  this  is  harmful,  if  anything,  for  it  affects  unfavorably 
both  the  possible  degree  of  compression  and  the  capacity  of  the 
machine.  The  cooler  the  mixture  after  formation  and  vaporiza- 
tion, the  better. 


CHAPTER   IX 

GAS-ENGINE    FUELS!    GAS   FUELS 

OUTSIDE  of  producer  gas,  which  has  been  treated  in  a  previous 
chapter,  the  gases  used  for  gas  engine  fuel  are: 

1.    Illuminating    gas.     2.  Oil    gas.     3.  Coke    oven    gas.     4. 
Blast  'furnace  gas.      5.   Acetylene.     6.   Water  gas.     7.   Natural 
gas. 

i.  Illuminating  Gas.  --  Illuminating  gas  is  made  by  dis- 
tilling bituminous  coal  in  retorts.  From  100  pounds  of  average 
coal  are  obtained  about  400-450  cu.  ft.  of  cooled  gas,  50-70  Ib. 
of  coke,  4.25-4.75  Ib.  of  tar,  and  8-10  Ib.  of  ammonia  liquor. 
Each  100  pounds  of  coal  also  require  about  20  pounds  of  coke 
for  the  heating  of  the  retort. 

The  composition  of  the  gas  varies  constantly  somewhat  even 
in  the  same  plant.  The  average  composition  is  about  45-48  per 
cent  by  volume  of  hydrogen,  35-38  per  cent  CH4,  5-8  per  cent  CO, 
and  the  rest  heavy  hydrocarbons,  oxygen,  nitrogen,  and  carbon 
dioxide.  The  gas  owes  its  illuminating  power  to  the  heavy 
hydrocarbons  it  contains.  Its  heating  value,  however,  is  not 
proportional  to  its  candle  power.  To  determine  the  heating 
value  the  best  way  is  to  use  a  calorimeter.  It  may,,  however, 
with  sufficient  accuracy  be  computed  from  the  analysis  of  the 
gas.  Varying  somewhat  in  this  same  locality,  the  average  lower 
heating  value  is  probably  not  far  from  600  B.  T.  U.  per  cubic  foot. 
Its  density  averages  about  .4,  air  being  1.0,  its  average  weight 
per  cubic  foot,  therefore,  being  not  far  from  .032  Ib. 

The  following  table  shows  a  few  typical  analyses  of  illuminat- 
ing gas.* 

*  Mostly  from  Poole,  the  Calorific  Power  of  Fuels. 
206 


GAS-ENGINE    FUELS 


207 


H 

CH4 

Hydro- 
carbons 

C02 

CO 

O 

N 

B.T.U. 
cu.  ft. 
Lower 
Value 

Newton,  Mass  
Cleveland               

50.59 
34.80 

34.80 

28.80 

5.23 
11.20 

1.16 
.20 

6.16 
10  40 

40 

2.06 
14  20 

599 
657 

Boston 

47.49 

38.67 

5.21 

1  04 

6  74 

85 

651 

Cincinnati    

45.85 

39.26 

5.17 

.82 

4.78 

41 

3.71 

645 

Birmingham    

40.23 

39.00 

4.76 

1.50 

4.05 

36 

10  10 

671 

Glasgow 

39.18 

40.26 

1000 

29 

7  14 

06 

3  0 

8301 

Liverpool  

36.44 

44.28 

7.90 

1  70 

3.39 

1P 

6.10 

7921 

Hanover  
Paris 

46.27 
50.10 

37.55 
33.10 

3.17 
5.80 

.81 
1  50 

11.19 
630 

50 

1.01 
2  70 

661 

667 

Average 

f  43.44 

3730 

6  49 

1  00 

6  68 

32 

5  77 

686 

2.  Oil  Gas.  —  Oil  gas  is  made  by  vaporizing  and  superheat- 
ing crude  oils.  It  may  be  made  by  vaporizing  these  oils  in  retorts 
which  are  externally  heated,  as  in  the  case  of  the  Pintsch  method, 
or  the  manufacture  may  be  carried  on  as  in  the  Lowe  process,  in 
which,  as  previously  described,  the  generator  is  first  internally 
heated  by  burning  crude  oil,  the  oil  to  be  gasified  being  then  sent 
into  the  heated  chamber  together  with  steam  under  exclusion  of 
air. 

Pintsch  gas,  much  used  for  railway  car  illumination,  contains, 
according  to  Giildner,* 

17.4  per  cent  C2H4,  58.3  per  cent  CH4,  and  24.3  per  cent  H  by 
volume. 

Another  gas  obtained  from  a  by-product  paraffin  oil  showed 
the  following  composition  by  volume: 

28.9  per  cent  C2H4,  54.9  per  cent  CH4,  5.6  per  cent  H,  8.9  per 
cent  CO,  and  9  per  cent  CO2. 

Oil  gas  as  made  by  the  Lowe  process  is  a  water  gas ;  the  com- 
position will  therefore  show  much  more  H  than  is  indicated  in  the 
above  analysis  of  Pintsch  gas. 

Wyer  f  in  his  Gas  Producer  gives  the  following  figures : 

32  per  cent  H,  48  per  cent  CH4,  16i  per  cent  C2H4,  3  per  cent 
N,  .5  per  cent  O. 

1  Values  evidently  too  high. 

*  Giildner,  Entwerfen  und  Berechnen  der  Verbrennungsmotoren. 

f  Wyer,  Producer  Gas  and  Gas  Producers. 


208  INTERNAL  COMBUSTION  ENGINES 

Giildner  estimates  that  the  yield  of  gas  from  1  pound  of  oil  in 
the  Pintsch  process  is  from  7-10  cu.  ft.  of  cooled  gas,  about  .75 
Ib.  of  coke  being  used  in  the  same  time  for  heating.  This  amounts 
to  about  100  Ib.  of  oil  or  about  14  gallons  of  oil  per  1000  cu.  ft. 
of  gas,  in  the  most  favorable  case,  as  against  9-10  gallons  per  1000 
cu.  ft.  in  the  Lowe  process.  The  heating  value  per  cubic  foot  of  the 
Pintsch  gas,  however,  is  higher  than  that  of  the  Lowe  in  the  ratio 

900 

of  about  - — ,  so  that  on  the  basis  of  thermal  efficiency  the  two 
650 

methods  of  making  oil  gas  are  probably  not  very  far  apart,  with 
the  chances  in  favor  of  the  Lowe  system  on  account  of  the  coke 
used  for  heating  in  the  other  system,  which  must,  of  course,  be 
considered  in  making  thermal  calculations. 

3.  Coke  Oven  Gas.  —  Coke  oven  gas  when  made  in  the  old 
type  Bee-hive  oven  is  fundamentally  the  same  as  illuminating 
gas.  Compare  the  following  analysis  given  by  Wyer  of  a  sample 
of  this  gas  with  the  average  analysis  given  for  illuminating  gas 
on  page  208. 

H,  50.0  per  cent;  CH4,  36.0  per  cent;  C2H4,  .4  per  cent;  N,  2  per 
cent;  CO,  6  per  cent;  O,  5  per  cent;  CO2,  1.5  per  cent. 

When  made  in  modern  by-product  ovens,  however,  the  gas 
yield  is  sometimes  divided  and  that, part  of  the  gas  used  for  fuel 
has  a  somewhat  different  composition.  From  a  diagram  published 
by  the  United  Coke  and  Gas  Company  of  New  York,*  it  appears 
that  the  gas  evolved  during  the  coking  of  the  charge  in  a  retort  is 
divided  into  two  parts.  The  entire  coking  period  covers  nearly  25 
hours.  The  gas  evolved  during  approximately  the  first  ten  hours, 
called  the  surplus  or  rich  gas,  is  separated  from  that  made  during 
the  rest  of  the  period,  called  fuel  gas.  The  surplus  gas  is  high  in 
illuminating  power  and  in  heating  value,  approximately  720 
B.  T.  U.  per  cubic  foot.  The  fuel  gas  has  an  average  heating  value 
of  about  560  B.  T.  U.  per  cubic  foot.  The  figures  quoted  are  for  a 
medium  volatile  coal.  The  rich  gas  from  a  ton  of  this  coal  in  an 
actual  case  amounted  to  4300  cubic  feet,  which  was  46  per  cent 
of  the  total  yield  per  ton,  this  part  of  the  gas  carrying  52  per  cent 
of  the  total  heat  value  of  the  gas.  A  ton  of  this  coal  therefore 
yields  about  9400  cu.  ft.  of  gas. 

The  same  treatise  above  quoted  gives  the  following  gas 
*  The  United  Otto  System  of  By-product  Coke  Ovens. 


GAS-ENGINE  FUELS 


209 


analysis   for  a  coal   carrying    from    30-32  per  cent  of  volatile 
matter: 


Illuminating 
or  Rich  Gas 

Fuel  Gas 

Illuminants 

58 

28 

CH4    

40.8 

29.6 

H                                                    

37.6 

41.6 

CO 

5.6 

6.3 

CO2             

3.7 

3.2 

o        

.4 

.4 

N 

6  1 

16.1 

B  T  U  per  cu  ft  higher  value 

100.0 
7303 

100.0 
551.3 

Where  no  illuminating  gases  are  desired  the  entire  gas  yield 
is  recovered  together.  The  gas  is  excellent  for  power  purposes 
except  for  the  somewhat  high  percentages  of  H  which  render  the 
fuel  mixtures  liable  to  pre-ignition  under  high  compression  in  the 
cylinder. 

4.  Blast  Furnace  Gas.  —  The  blast  furnace  is  really  a  large 
gas  generator,  with  the  difference  that  to  the  charge  of  fuel  is 
added  the  burden  of  ore  and  of  flux,  and  that  the  blast  is  air  alone 
without  admixture  of  steam.  Owing  to  the  calcination  of  the 
flux,  which  is  limestone  ordinarily,  and  to  the  fact  that  no  steam 
is  used,  the  gas  is  high  in  CO2  and  contains  little  H,  the  main 
combustible  being  CO.  This  gas  had  been  used  a  long  time  in 
hot  blast  stoves  for  blast  heating  and  under  boilers  to  produce 
steam  for  power  purposes  around  the  works.  It  was  Thwaite  in 
England  and  Liirman  in  Germany  who  about  twenty  years  ago 
called  attention  to  the  fact  that  this  gas,  although  low  in  heating 
value,  could  be  readily  burned  in  gas  engines  when  suitably  com- 
pressed. The  credit  of  having  carried  out  this  idea  first  on  a  large 
scale  belongs  to  the  Societe  Cockerill  of  Seraing,  Belgium,  who 
about  1898  put  a  150  horse-power  engine  using  this  gas  into 
operation. 

It  is  estimated  roughly  that  for  every  ton  of  pig  iron  produced 
one  ton  of  coke  is  required,  the  combustion  resulting  in  about 
5  tons  of  gas.  Taking  a  furnace,  therefore,  with  an  average  daily 
capacity  of  200  tons  of  pig  iron,  the  gas  available  per  hour  amounts 


210  INTERNAL  COMBUSTION  ENGINES 

to  about  41.6  tons  or  1,000,000  cu.  ft.  Estimating  that  500,000 
cubic  feet  are  necessary  for  the  operation  of  the  hot  blast  stoves, 
this  leaves  500,000  cu.  ft.  available,  which  if  directly  used  in  gas 
engines  would  develop  about  5000  I.  H.  P.  Of  this  amount  1000- 
1200  horse-power  are  probably  required  for  power  purposes 
around  the  furnace,  leaving  from  3800-4000  horse-power  avail- 
able for  other  work.  The  same  amount  of  gas,  if  used  under  boilers, 
would  have  resulted  in  only  about  1200  boiler  horse-power,  or 
perhaps  about  2400  horse-power  total  in  steam  engines,  leaving 
1200  horse-power  available  for  other  purposes. 

The  composition  and  heating  value  of  blast  furnace  gas  natu- 
rally varies  somewhat  in  different  furnaces,  and  even  in  the  same 
furnace  under  varying  accidental  conditions  of  operation.  A  large 
number  of  determinations  led  M.  Witz  *  to  the  conclusion  that 
the  average  heating  value  of  a  standard  cubic  foot  was  110  B.  T.  U. 
and  that  it  very  rarely  fell  be'low  95  B.  T.  U.,  or  rose  above  118 
B.  T.  U. 

The  average  composition  of  the  gas,  according  to  Ledebur, 
appears  to  be 


%  by  Volume  by  Weight 

CO 24.0  24.0 

CO2 12.0  17.0 

H    .  . 2.0  .2 

CH4 2.0  .8 

N  .  60.0  58.0 


The  above  analysis  shows  no  water  vapor,  some  of  which  is 
present  in  the  gas  as  it  leaves  the  stack,  and  it  therefore  probably 
refers  to  cleaned  gas.  It  is  apparent  that  it  is  an  excellent  gas 
for  internal  combustion  engines.  Its  low  content  of  H  makes  it 
suitable  for  high  compressions,  thereby  overcoming  any  objec- 
tion that  may  be  made  regarding  its  low  heating  value  and 
difficulty  of  ignition. 

The  most  serious  trouble  encountered  in  the  use  of  blast  fur- 
nace gas  is  the  fact  that  it  carries  more  or  less  dust,  which  renders 
cleaning  of  the  gas  imperative  before  use  in  engines.  It  is  also 
apt  to  carry  metallic  vapors,  which  do  not,  however,  become 

*  Moteurs  a  Gaz  et  a  Pet  role,  p.  267. 


GAS-ENGINE  FUELS  211 

harmful  until  after  combustion  in  the  cylinder.  The  amount  of 
impurities  carried  depends  altogether  upon  the  kind  of  ore  re- 
duced in  the  furnace.  In  some  cases  it  is  so  slight  that  the  ordi- 
nary dust  settlers  combined  with  a  scrubber  of  some  sort  are 
quite  sufficient  to  reduce  the  amount  to  below  the  allowable 
limit.  This  is,  however,  the  exception,  and  the  fact  that  the  gas 
must  be  cleaned,  and  thoroughly  cleaned,  cannot  be  emphasized 
too  strongly.  , 

It  is  comparatively  easy  to  take  out  the  coarser  dust  carried 
by  the  gas  by  appliances  which  have  long  been  in  use  for  this 
purpose  to  prepare  the  gas  for  stoves  and  boilers.  The  fine  dust, 
however,  causes  more  trouble,  and  special  cleaning  apparatus  is 
necessary  to  reduce  the  amount  carried. 

The  ordinary  method  of  procedure  is  to  give  the  gas  a  prelim- 
inary cleaning  by  allowing  the  coarse  dust  to  settle.  The  fine 
dust,  together  with  the  water  vapor  and  the  metallic  vapors,  are 
then  taken  out  by  passing  the  gas  through  washers,  of  which 
there  are  various  forms,  as  spray  towers,  centrifugal  fans,  etc. 
Coke  scrubbers  are  not  satisfactory  on  account  of  the  clog- 
ging up  by  dust  which  soon  takes  place.  A  dry  scrubber, 
filled  with  sawdust  or  shavings,  is  sometimes  used  to  complete 
the  outfit  of  cleaning  apparatus.  The  amount  of  water  used 
in  the  washers  varies  with  different  types.  It  may  be  from 
5-50  gallons  per  1000  cu.  ft.  of  gas  cleaned,  depending  upon 
the  efficiency  of  the  apparatus.  The  amount  of  dust 
finally  carried  by  the  gas  should  not  be  higher  than  about 
.2  grains  per  cubic  foot. 

5.  Acetylene.  —  It  is  only  in  recent  years  that  the  means 
for  making  acetylene  gas  in  any  quantity  were  found.  To-day 
calcium  carbide  is  made  in  quantity  in  the  electric  furnace.  The 
gas  is  produced  by  decomposing  this  carbide  by  means  of  water, 
as  per  following  reaction: 

CaC2  +  2  H2O  =  C2H2  +  CaOH2O 

The  generators  employed  usually  regulate  the  amount  of  water 
supplied  to  the  carbide  receptacle.  The  gas  is  led  to  a  holder, 
which  by  the  position  of  its  bell  regulates  the  water  supply.  The 
amount  of  gas  produced  per  pound  of  carbide  should  be  theoreti- 
cally 5.45  cu.  ft.  of  dry  acetylene  gas.  Owing  to  impurities,  how- 


212  INTERNAL  COMBUSTION   ENGINES 

ever,  this  is  usually  reduced  to  about  4.8  cu.  ft.     Combustion  of 
this  gas  takes  place  according  to  the  formula 

C2H2  +  5O  -  H20  +  2CO2 

Its  heating  value  is  20673  B.  T.  U.  per  pound,  or  1499  B.  T.  U. 
per  cubic  foot  lower  value. 

The  gas  is  distinguished  by  low  temperature -of  ignition,  lower 
than  that  of  H,  approximately  865  degrees  Fahrenheit,  high 
velocity  of  flame  propagation  at  the  best  ratio  of  air  to  gas,  about 
12  to  1,  and  high  maximum  temperature  of  explosion  owing  to 
the  high  heating  value.  The  first  of  these,  low-ignition  tempera- 
ture, leads  to  pre-ignition  and  requires  the  use  of  comparatively 
low  compression  pressures. 

6.  Water  Gas.  —  The  theory  of  the  production  of  water  gas 
has  been  already  outlined  in  a  previous  chapter.     The  average 
composition  of  the  gas  may  be  taken  to  approximate  by  volume 
42  per  cent  CO,  44.5  per  cent  H,  3.5  per  cent  CO2,  the  rest  being 
O  and  N. 

In  medium  sized  well-handled  generators  each  pound  of  coke 
will  yield  about  32  cu.  ft.  of  gas,  each  pound  of  good  anthracite 
coal  from  24-30  cu.  ft.  The  average  lower  heating  value  of  the 
gas  may  be  taken  at  290  B.  T.  U.  per  cu.  ft. 

7.  Natural  Gas.  —  Natural  gas  is  found  in   many  parts  of 
the  world.     It  has,  however,  perhaps  received  the  most  extended 
use  as  a  fuel  for  power  in  the  United  States.     It  is  there  found  in 
New  York,  Pennsylvania,  Ohio,  Indiana,  West  Virginia,  Kentucky, 
Tennessee,  Colorado  and  California.     This  gas  is  not  of  constant 
chemical   composition  in  the  different   wells,   and   not   constant 
even  in  the  same  well.     Marsh  gas,  CH4,  however,  is  nearly  always 
the  main  constituent.     According  to  Poole,  the  Ohio  and  Indiana 
fields  yield  a  gas  of  the  most  constant  composition.     The  follow- 
ing is  the  composition  at  Findlay,  Ohio,  and  is  typical  of  the 
field. 

H          CH4      C2H4       O       CO       CO2        N        H2S 
1.64        93.35        .35        .39        .41        .25        3.41        .20  per  cent  by  vol. 

The  above  composition,  however,  is  sometimes  radically 
changed.  Thus  a  gas  well  near  Pittsburg  changed  the  composi- 


GAS-ENGINE    FUELS 


213 


tion  of  the  gas  in  three  months  from  9.64  per  cent  H  to  35.92  per 
cent  H,  mostly  at  the  expense  of  Marsh  gas. 

The  heating  value  of  this  gas  is  high,  the  above  Findlay  gas 
showing  a  lower  heating  value  of  962  B.  T.  U.  per  cubic  foot  as  com- 
puted. It  is  a  good  fuel  for  gas  engines,  as  it  is  cheap  and  not 
very  liable  to  pre-ignition  when  the  hydrogen  is  low.  It  is,  how- 
ever, of  decreasing  importance  on  account  of  the  gradual  failure 
of  the  supply. 

The  following  table,  and  Fig.  9-1,  give  a  recapitulation  of  the 
most  important  data  for  the  fuel  gases  most  often  found  in  gas 
engine  practice.  It  is  to  be  remembered  that  the  figures  given 
represent  approximate  average  results  only,  but  for  rapid  calcula- 
tion they  are  sufficiently  accurate. 


AVERAGE  APPROXIMATE  DATA  FOR  FUEL  GASES 


Wt.  per 

Lower 

Least  air 

No. 

cu.  ft. 
Standard 

Density 

Heating 
Value 

required  for 
Combustion 

Kind  of  Gas 

in 

Air  =  l 

per  cu.  ft. 

cu.  ft. 

pounds 

B.  T.  U. 

per  cu.  ft. 

1 

Illuminating  gas 

.032 

.40 

565 

5  25 

Natural  gas    

.045 

.55 

950 

9.10 

3 

Blue  water  gas  .  

.057 

.71 

290 

2.45 

4 

Oil  gas   Pintsch 

.056 

.70 

1000* 

9  50 

5 

Oil  gas,  Lowe  

.040 

.49 

650 

7.75 

6 

Coke  oven  gas              .    .        

.029 

.36 

545 

5.00 

7 

Producer  gas  from  coke 

075 

.93 

135 

1  00 

8 

Producer  gas  from  anthracite   .... 

.065 

.80 

145 

1.15 

9 

Producer  gas  from  soft  coal  

.073 

.90 

145 

1.25 

10 

Blast  furnace  gas 

079 

98 

100 

.70 

214 


INTERNAL  COMBUSTION   ENGINES 


grains 

<| 

e 


P 


1L| 


si 


II 

«  i 

CO      P^ 
OQ      O 

o  "I 


a 
a 

3 

<D 


0-      H        C* 

M 


LO        O         *'         30         Ci         O 


CHAPTER  X 

THE   FUEL    MIXTURE,    EXPLOSIBILITY,    PRESSURE,    TEMPERATURE 

i.  Explosibility.  —  When  we  mix  a  combustible  gas  or 
vapor  with  air  there  result  explosive  mixtures  if  certain  ratios 
of  air  to  combustible  are  used  in  each  case.  For  each  of  these  vari- 
ous mixtures  the  products  of  combustion  attain  certain  pressures 
and  temperatures  under  the  same  conditions.  It  is  also  found 
that  the  time  interval  between  ignition  and  attainment  of  highest 
pressure  varies  with  the  ratio  of  mixing,  i.e.,  that  the  velocity  of 
flame  propagation  differs.  , 

That  mixture  in  which  just  enough  oxygen  is  present  to  com- 
plete the  combustion  of  the  charge  of  gas  or  of  vapor  shows  the 
highest  explosive  pressures  and  temperatures,  and  also  very 
nearly  the  highest  velocity  of  flame  propagation.  Queer,  and  as  yet 
not  explained,  is  the  fact  that  according  to  Clerk  the  highest 
velocity  of  propagation  is  found  when  the  gas  is  a  little  in  excess 
of  the  theoretical  ratio  in  the  mixture. 

As  the  proportion  of  oxygen  or  of  air  is  decreased  from  or 
increased  beyond  the  theoretical  amount  for  complete  combus- 
tion, the  resulting  maximum  pressures  and  temperatures  are  not 
so  high,  the  explosion  occurs  more  and  more  slowly,  until,  at  the 
outside  limits  of  explosibility,  it  approximates  slow  combustion. 

There  is  therefore  a  range  of  mixtures  for  each  gas  and  vapor 
in  which  range  the  mixture  is  explosive.  When  there  are  con- 
stituents present  other  than  those  resulting  from  mixtures  of  gas 
or  vapor  and  air,  such  as  burned  gases,  the  results  are  again  modi- 
fied. 

The  following  table  shows  the  volume  of  air  required  per 
cubic  foot  of  various  gases,  under  standard  conditions,  for  com- 
plete combustion,  i.e.,  for  what  might  be  called  the  true  explosive 
mixture.  To  facilitate  computation  to  a  weight  basis,  a  column 
giving  the  density  of  the  gases  or  vapors  with  air  =  1  =  0.08072 

215 


216 


INTERNAL  COMBUSTION  ENGINES 


pounds  per  cubic  foot  standard  is  added.  The  table  also  shows 
average  heating  values,  and  finally  the  heating  value  of  the  true 
explosive  mixture.  It  will  be  noted  that  the  heating  values  of 
the  mixtures  show  much  less  difference  than  do  the  gases  them- 
selves. 


Av.  lower 

heating 

Vol.  of  Air 

Density 

Av.  lower 

value 

for  true 

of  gas 

heating 

of  true 

explosive 
mixture 
cu.  ft. 

Air  =  1 
=  .08072 
Ibs. 

value 
of  gas 
B.  T.  U. 

explosive 
mixture 
B.  T.  U. 

per 

per 

per 

cu.  ft. 

cu.  ft. 

cu.  ft. 

CO 

2  35 

967 

342 

102 

H    

2.35 

.069 

297 

89 

CH4 

9.60 

.554 

952 

90 

C,Ho  

11.75 

.915 

1499 

118 

14.10 

.974 

•   1564 

103 

Av  natural  gas 

9.00 

880 

88 

Av.  illuminating  gas    

5.25 

.40 

560 

90 

Av.  water  gas                 

2.30 

.72 

290 

87 

Av.  producer  gas  from  coke  

1.00 

.93 

135 

68 

Av.  producer  gas  from  anthracite  .... 

1.15 

.80 

145 

68 

Coke-oven  gas                                   .... 

5.00 

.36    . 

545 

91 

Blast-furnace  gas 

'     70 

98 

100 

59 

To  give  volume  ratios  for  the  liquid  fuels  is  not  so  easy,  because 
the  volume  of  vapor  obtained  from  a  certain  weight  of  a  liquid 
fuel  is  not  constant  but  depends  upon  the  temperature.  Experi- 
ments along  this  line  are  not  numerous.  Those  made  indicate 
that  for  light  and  medium  heavy  oils  there  is  a  200-fold  increase 
in  the  original  volume  at  ordinary  temperatures,  while  the  in- 
crease is  about  400  fold  at  the  ordinary  vaporizer  temperature. 
It  appears  also  that  for  heavy  oils  a  temperature  exceeding 
1400  degrees  is  required  to  anywhere  near  complete  vaporization. 
This  explains  in  part  the  difficulty  encountered  in  the  use  of  crude 
oil  in  vaporizers.  With  the  above  increase  in  volumes  the  ratio 
of  air  to  oil  vapor  by  volume  probably  is  in  most  cases  between 
25  and  30. 

It  is  much  more  usual,  however,  to  calculate  the  air-liquid 
fuel  ratios  by  weight.  This  ratio  for  the  petroleum  oils  is  approxi- 


THE  FUEL  MIXTURE 


217 


mately  15,  and  for  alcohol  about  9,  for  the  true  explosive  mixture. 
To  get  some  idea  of  the  heating  value  per  cubic  foot  of  the  explo- 
sive mixture  the  volume  added  to  the  air  by  the  vapor  is  some- 
times neglected.  This  gives  results  which  are  close  enough  for 
most  purposes.  In  the  following  table,  however,  account  has 
been  taken  of  the  vapor  volume  by  assuming  a  300-fold  increase 
in  the  volume  of  the  liquid  due  to  vaporization: 


Weight  of  air 

Average 

Average 
lower 

Liquid  Fuel 

required 
perlb. 
of 

Av.  Sp. 
Gr. 
at 

lower 
heating 
value 

heating 
value 
per 

fuel 

60°  F 

per  Ib. 

cu.  ft. 

for  true 

H2O  =  1.0 

of 

of  true 

explosive 
mixture 

fuel 
B.  T.  U. 

explosive 
mixture 

B.  T.  U. 

Heavy  Pa.  crude    

.886 

19210 

99  2 

Light  Pa.  crude    

.826 

17930 

92  0 

Heavy  W.  Va.  crude  

Approximately 

.873 

18320 

94.6 

Light  W.  Va.  crude  

.841 

18400 

95.0 

Kerosene 

1501b 

80 

18520 

qcj  o 

74° 

.69 

Gasoline 

19000 

07  7 

69° 

.71 

Benzol,  C6H6          .    ... 

134 

866 

17190 

99  3 

Alcohol,  100  per  cent  

8.6 

.794 

11664 

103.0 

Alcohol,  90  per  cent    

7.8 

.815 

10080 

104.0 

To  make  sure  of  complete  combustion  of  the  charge,  which  is 
one  of  the  primary  objects,  it  is  not  usual,  however,  to  work  with 
the  theoretic  air  supplies  above  computed,  mainly  because  a 
perfect  mixture  is  hardly  ever  obtained.  An  excess  of  air  is 
therefore  employed  in  nearly  all  cases.  This  acts  beneficially  in 
several  other  ways.  The  maximum  explosion  temperatures  are 
reduced,  and  pre-ignition  is  rendered  less  likely.  Especially  is 
this  noticeable  with  a  gas  carrying  much  hydrogen  or  with  acety- 
lene. The  only  limit  set  to  the  amount  of  excess  air  that  can  be 
used  is  the  limit  of  the  explosive  range  of  the  particular  gas  or 
vapor.  But  this  range  is  in  most  cases  so  wide  that  in  practice 
the  limit  is  rarely  reached.  Under  full  load  an  excess  of  air  of 
from  30-40  per  cent  is  usual,  and  for  the  rich  mixtures  even  more 
may  be  used.  This  excess  decreases  the  heating  value  of  the 


218 


INTERNAL  COMBUSTION    ENGINES 


mixture  correspondingly  below  those  computed  above   for  the 
true  explosive  mixtures. 

The  amount  of  excess  air  any  given  gas  can  carry  and  still 
form  an  explosive  mixture  varies  with  the  kind  of  gas.  Experi- 
ments have  been  made  not  only  on  pure  gas-air  mixtures*  under 
ordinary  conditions  of  pressure  and  of  temperature,  but  also  on 
mixtures  to  which  had  been  added  inert  gases,  as  CO2,  to  test  the 
effect  burned  gases  would  have  upon  a  fresh  charge.  The  follow- 
ing table  shows  the  upper  and  lower  limits  of  explosibility  for 
some  of  the  most  common  gases,  together  with  the  theoretical 
ratio.  It  is  hardly  necessary  to  point  out  that  the  real  lower 
limit  of  operation,  as  far  as  economy  is  concerned,  is  the  theoreti- 
cal ratio: 


Volume  of  air  per  unit 
volume  of  gas  for 

CO 

H 

C2H2 

CH4 

C6H6 

Ave. 
111.  gas 

Gaso- 
line 

Upper  explosive  limit  .... 
Theoretical  ratio    

5.1 
2.35 

9.6 
2.35 

28.6 
11.75 

15.4 
9.60 

36.7 
25-30 

11.7 
5.25 

40.7 
25-30 

Lower  explosive  limit  .... 

.33 

.51 

.91 

6.81 

14.38 

4.24 

19.41 

Dr.  Eitner's  results  have  been  graphically  represented  in 
Fig.  10-1  by  F.  E.  Junge  and  published  in  Power  for  August,  1906. 
From  this  diagram  it  can  be  seen  at  a  glance  how  much  wider  the 
explosive  range  is  for  some  fuels  than  for  others.  Thus,  for  in- 
stance, one  cubic  foot  of  mixture  will  be  explosive  under  ordinary 
conditions  of  pressure  and  temperature  when  it  contains  any- 
where between  16  and  74  per  cent  of  CO,  a  range  of  58  per  cent. 
The  range  for  illuminating  gas  is  11.2  per  cent,  and  for  gasoline 
only  2.5  per  cent. 

Regarding;  the  experiments  with  admixtures  of  inert  gases, 
it  can  be  said  in  general  that  the  result  is  a  narrowing  of  the  ex- 
plosive range,  i.e.,  the  effect  is  harmful.  Raising  the  tempera- 
tures of  mixtures  thus  contaminated  has  a  noticeably  beneficial 
effect  in  the  case  of  hydrogen  and  illuminating  gas  mixtures  only. 
Regarding  the  effect  upon  the  explosive  limits  of  increasing  the 
initial  pressure  of  the  mixture,  nothing  definite  is  known. 

Carbon  monoxide  and  hydrogen  are  the  two  most  important 
*  Professor  Eitner,  in  the  Journal  fur  Gasbeleuchtung,  1902. 


THE  FUEL  MIXTURE 


219 


constituents  found  in  our  power  gases,  and  the  question 
as  to  the  most  desirable  amount  of  each  of  these  in  the 
gas  has  often  been  raised.  This  point  is  taken  up  by  F.  E. 
Junge  *  as  follows : 

"The  temperature  at  which  hydrogen  ignites  is  considerably 
below  that  of  carbon  monoxide,  and  the  rapidity  of  flame 


£    80 


y///, 

mbustiori 


II 


FIG.  10-1. 


tion  at  atmospheric  pressure  is  about  30  times  greater.  Its 
diffiusion  properties  are  by  far  more  favorable  than  those  of  car- 
bon monoxide,  so  that  its  admixture  with  air  is  accomplished  in 
a  much  shorter  time.  Its  presence,  therefore,  determines  the 
manner  of  ignition  and  the  temperatures  prevailing  at  various 
points  of  the  inner  walls.  On  the  other  hand,  minor  variations 
*  Power,  August,  1906. 


220  INTERNAL  COMBUSTION  ENGINES 

in  the  hydrogen  content  are  of  great  influence  on  the  speed  of 
ignition  or  rather  of  flame  propagation  throughout  the  whole 
mixture,  and  therefore  on  engine  output  and  consumption. 

"  A  gas  to  be  of  ideal  composition  for  the  engine  builder  must, 
therefore,  not  contain  too  much  hydrogen,  so  as  not  to  make  the 
engine  over-sensitive  to  premature  explosions,  but  enough  so  as 
to  assist  the  slow  and  after-burning  carbon  monoxide,  and  to 
accelerate  flame  propagation  throughout  the  mixture." 

2.  Pressure  and  Temperature  after  Combustion.  —  It  has 
already  been  mentioned  that  the  pressures  and  temperatures 
realized  in  explosive  combustion  are  not  as  high  as  those  cal- 
culated by  the  ordinary  method  of  assuming  specific  heat  con- 
stant. The  determination  of  the  causes  of  this  phenomenon  has 
always  been  a  favorite  subject  for  experimentation  with  investiga 
tors,  and  this  is  fully  warranted  by  its  importance  to  the  theory 
of  internal  combustion  engines.  It  will  hardly  be  necessary  to 
review  the  earlier  efforts  in  this  field.  For  them  the  reader  is 
referred  to  the  works  of  Clerk  *,  Grover  f,  Robinson  J,  Witz,§  and 
others.  The  subject  has  already  been  briefly  discussed  in  Chap- 
ter IV  of  this  book  under  the  head  of  "Combustion  and  Expan- 
sion Strokes."  The  entire  question  seems  on  analysis  to  narrow 
down  t!o  variation  of  specific  heat  -itnth  temperature  and  to  after- 
burning. Dissociation  as  one  of  the  causes  tending  to  produce 
the  effects  mentioned  is  now  regarded  by  most  writers  as  possible 
but  improbable. 

The  most  important  work  of  recent  years  along  the  lines 
under  discussion  has  been  done  by  Langen  ||  and  by  Clerk.  |  It 
would  seem  that  these  two  investigations,  combined  with  the 
earlier  one  of  Mallard  and  Le  Chatelier,  should  lead  to  some  fairly 
definite  conclusions.  They  will  therefore  be  reviewed  in  some 
greater  detail. 

Langen  in  his  experiments  used  a  cast-steel  spherical  vessel, 
about  15}  inches  in  diameter.  This  was  furnished  with  the  neces- 

.   *  Clerk,  The  Gas  and  Oil  Engine. 
f  Grover,  Modern  Gas  and  Oil  Engines. 
I  Robinson,  Gas,  Oil  and  Air  Engines. 
§  Witz,  Moteurs  a  Gaz  et  a  Petrole. 
||  A.  Langen,  Zeitschrift  d.  V.  d  I..  Vol.  47,  p.  622. 
If  D.  Clerk,  Proc.  of  the  Royal  Society,  A,  Vol.  77,  1906.' 


THE  FUEL  MIXTURE  221 

sary  connections  for  exhaust  pump,  gas  supply  cylinders,  indica- 
tor gages,  etc.  The  igniter  reached  to  the  center  of  the  sphere. 
The  vessel  itself  was  surrounded  by  a  water  bath  with  thermome- 
ters at  inlet  and  outlet,  so  that  the  temperature  of  the  body  of 
gas  in  the  vessel  could  be  accurately  determined.  The  indicator 
was  of  the  ordinary  type  except  that  the  oscillating  motion  of 
the  drum  was  changed  to  continuous  motion.  The  details 
of  the  entire  construction  were  very  ingenious.  The  press- 
ing of  a  single  button  sufficed,  by  electrical  means,  to  first 
press  the  pencil  against  the  drum,  and  immediately  afterward 
to  fire  the  charge.  It  was  only  necessary  to  break  the  current 
when  the  decrease  in  pressure,  due  to  cooling  of  the  burned 
gases,  had  become  so  small  in  two  revolutions  of  the  drum 
that  the  lines  interfered. 

The  method  of  test  was  to  exhaust  the  vessel  and  then  to  fill 
it  with  air  a  number  of  times  until  it  was  fair  to  assume  that  all 
burned  gases  from  a  previous  explosion  had  been  replaced.  The 
vessel  was  then  again  exhausted  to  such  a  degree  that,  by  filling 
with  combustible  gas  and  inert  gases  of  the  kind  desired,  the 
vessel  would,  at  atmospheric  pressure,  be  filled  with  combustible 
and  inert  gases  in  the  proportion  required.  After  enough  time 
had  been  given  for  diffusion  and  the  thermometer  showed  that 
constant  temperature  had  been  reached,  the  charge  was  fired  and 
the  diagram  taken. 

In  order  to  obtain  a  common  basis  for  comparison  with  the 
work  of  previous  experimenters,  Langen  recomputed  all  of  his 
results  and  those  of  Bunsen,  Berthelot  and  Vieille,  and  Mallard 
and  Le  Chatelier,  on  the  assumption  that  the  temperature  at  the 
moment  of  explosion  was  0  degrees  Centigrade.  Figs.  10-2  and 
10-3  *  show  graphically  the  results  of  all  of  these  experiments, 
the  first  for  CO,  the  second  for  H  as  the  fuel  gas.  In  the  diagrams 
TO  stands  for  the  ratio  of  explosion  pressure  observed  to  the  pres- 
sure before  ignition  if  the  temperature  of  the  fuel  mixture  is 
0  degrees  Centigrade  at  the  start,  m  is  the  ratio  of  the  volume 
of  inert  gases  compared  with  the  volume  of  fuel  gas.  These  inert 
gases  were  N,  O,  H  or  CO,  or  any  mixtures  of  these  four  as  indi- 
cated. The  results  marked  e  were  obtained  for  air-fuel  gas  mix- 
tures. 

*  Zeitschrift  d.  V.d.  L,  1903,  p.  623. 


222 


INTERNAL  COMBUSTION  ENGINES 


12 
11 

10 

b° 

ii     0 

s 

1   8 

rt       - 

\ 

\ 

\N 

\ 

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c 

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CO 

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s 

v 

TV 

'      X0 

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\ 

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\ 

s1 

*.y 

XJV 

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£2 

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Ratio  of  Explosion  to  Atn 

X0 

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Mui 

iird  t 

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ier 

£1 

heoveticnl  Kesult 
ests  by  Laiigen 

1     1 

1  3  4 

Ratio  of  Inert  Gases  to  Fuel  Gas;  (CO.)  by  Volume  =  »/t 

FIG.  10-2. 


\ 


re  to  Atm. 

o  -i 


Bunscn 
Berthelot 


Mallard  and  le  Chute 


|3 

I' 


1.  Theoretical  Result! 

2.  Tests  by  JUangen 


234  00 

Ratio  of  Inert  Gases  to  Fuel  Gas.^J )  by  Volume  =  'in 

FIG.  10-3. 


THE  FUEL  MIXTURE  223 

Langen,  in  analyzing  the  results  shown  in  the  above  diagrams, 
makes  the  following  observations: 

1.  The  computation  of  explosion  pressures  on  the  assumption 
of  constant   specific   heat   and   complete   combustion   furnishes 
values  which  considerably  exceed  those  actually  observed. 

2.  For  equal  ratios  of  inert  diatomic  gases  to  fuel  gases,  the 
kind  of  inert  gas  used  seems  to  have  no  influence  upon  the  explo- 
sion-pressure, as  far  as  the  same  observer  is  concerned.     This  would 
lead  to  the  conclusion  that  the  molecular  heats  of  the  so-called 
simple  or  diatomic  gases  are  equal  to  each  other,  at  least  up  to 
4500  degrees  Fahrenheit. 

Regarding  the  results  of  his  own  experiments,  Langen  is  of 
the  opinion  that  in  fuel  mixtures  containing  CO,  dissociation  of 
CO2  sets  in  when  the  temperature  exceeds  1900  degrees  Centigrade 
(3450  degrees  Fahrenheit).  He  bases  his  opinion  on  the  abnor- 
mal position  of  the  cooling  curve  as  observed  on  the  diagrams 
taken  for  such  mixtures.  And  since  the  amount  of  this  dissocia- 
tion is  indeterminate,  no  definite  equation  expressing  the  relation 
of  maximum  pressure  to  initial  pressure  can  be  established,  at 
least  for  temperatures  exceeding  3400.  For  hydrogen  mixtures, 
on  the  other  hand,  the  cooling  curves  on  the  diagrams  are  always 
normal.  Hence  the  dissociation  limit  for  steam  does  not  seem 
to  have  been  reached  even  with  the  strongest  mixtures. 

From  that  part  of  his  experiments  for  which  complete  com- 
bustion can  be  assumed,  Langen  derives  equations  for  mean 
molecular  heat  of  diatomic  gases,  and  for  carbon  dioxide  and 
steam.  The  temperature  limits  for  the  field  so  covered  are  not 
very  wide,  1500-1700  degrees  Centigrade  (2730-3100  degrees 
Fahrenheit),  and  further  it  was  assumed  that  the  molecular  heat 
is  a  linear  function  of  the  temperature.  Transposed  to  read  mean 
specific  instead  of  mean  molecular  heats,  these  equations  are  as 
follows : 

For  C02,  Cv  =  .152  +  .0000591  t. 
For  H2O,  Cv  =  .328  +  .000119  t. 
For  N,      Cv  =  .171  +  .0000215  *. 
For  O,       Cv  =  .150  +  .0000188  t. 

where  t  is  in  degrees  Centigrade. 

The  formula    of  Mallard  and   Le  Chatelier  agree  with   the 


224  INTERNAL  COMBUSTION  ENGINES 

above  as  regards  the  diatomic  gases,  O  and  N.  For  CO2  and 
H2O  these  observers  obtained  results  which  gave  the  following 
relations : 

For  CO2,  Cv  =  .143  +  .0000834  t. 
For  H2O,  Cv  =  .312  +  .000182  t. 

These  formulae  show  a  somewhat  more  rapid  increase  of  Cv 
with  temperature  than  do  those  of  Langen.  Langen  observes  in 
explanation  of  this  discrepancy  that  Mallard  and  Le  Chatelier's 
formula  for  CO2  is  obtained  from  results  for  which  the  tempera- 
tures were  from  1700  to  2000  degrees  Centigrade,  and  that  the 
formula  for  H2O  is  based  on  experiments  for  which  the  tempera- 
tures were  very  much  higher  than  for  his  experiments.  In  the 
former  case  dissociation  was  shown  to  be  more  than  likely,  in  the 
latter  the  formula  gives  results  which  do  not  seem  to  apply  very 
closely  for  the  important  temperature  range  between  2250  and 
4000  degrees  Fahrenheit.  It  is  plain,  therefore,  that  Langen's 
formulae  promise  greater  accuracy. 

The  second  important  investigation  in  this  field  was  made  by 
Clerk,  and  by  him  reported  to  the  Royal  Society.  His  method  of 
operation  is  so  decidedly  different  from  that  of  Langen  and  the 
earlier  experimenters  that  it  becomes  both  interesting  and  im- 
portant to  see  how  far  his  results  agree  with  those  already  men- 
tioned. 

The  method  of  experiment  is  best  described  in  Clerk's  own 
words : 

"It  consists  in  subjecting  the  whole  of  the  highly  heated 
products  of  the  combustion  of  a  gaseous  charge  to  alternate  com- 
pression and  expansion  within  the  entire  cylinder  while  cooling 
proceeds,  and  observing  by  the  indicator  the  successive  pressure 
and  temperature-falls  from  revolution  to  revolution,  together 
with  the  temperature  and  pressure  rise  and  fall  due  to  alternate 
compression  and  expansion.  The  engine  is  set  to  run  at  any  given 
speed,  and  at  the  desired  moment  after  the  charge  of  gas  and  air 
has  been  drawn  in,  compressed,  and  ignited,  the  exhaust  valve 
and  charge  inlet  valves  are  prevented  from  opening,  so  that  when 
the  piston  reaches  the  termination  of  its  power  stroke,  the  ex- 
haust gases  are  retained  within  the  cylinder,  and  the  piston  com- 
presses them  to  the  minimum  volume,  expands  them  again  to 


THE  FUEL  MIXTURE 


225 


the  maximum  volume,  and  so  compresses  and  expands  during 
the  desired  number  of  strokes." 

To  attempt  to  explain  the  method  of  evaluating  the  expansion 
and  compression  lines  so  obtained  would  lead  too  far  for  the  scope 
of  this  book.  The  reader  is  referred  to  the  original  article.* 

The  engine  operated  with  coal  gas.  The  average  composition 
of  the  working  fluid,  as  calculated  from  the  analysis  of  the  gas, 
was  H2O  (assumed  gaseous),  11.9  per  cent  by  volume;  CO2,  5.2 
per  cent;  O,  7.9  per  cent,  and  N,  75  per  cent.  The  mixture  as 
actually  used  varied  somewhat  from  this  composition,  but  since 
the  percentage  of  N  is  nearly  constant,  this  variation  can  have  but 
small  effect  upon  any  specific  heat  calculations. 

For  this  mixture,  Mr.  Clerk,  on  the  basis  of  his  experiments, 
found  the  following  mean  specific  heats,  expressed  in  foot  pounds 
per  cubic  foot  of  working  fluid  at  760  mm.  and  0°  C. 


Range  of  Temperature 
°C 

°F 

Mean  specific  heat  in  ft.  Ibs. 
per  cu.  ft.  at  760  mm  and  0°  C. 

0-   100 

32- 

212 

20.3 

0-  200 

32- 

392 

20.9 

0-  400 

32- 

752 

21.9 

0-   600 

32- 

1132 

22.8 

0-   800 

32- 

1472 

23-6 

0-1000 

32- 

1832 

24-6 

0-1200 

32- 

2192 

24.6 

0-1400 
0-1500 

32- 
32- 

2552 
2732 

25.0 
25.2 

Now  to  compare  these  results  with  those  of  Mallard  and  Le 
Chatelier  and  of  Langen,  the  easiest  way  would  be  to  reduce  them 
to  the  ordinary  specific  heat  basis,  and  then  to  compute  a  series 
of  specific  heats  for  the  same  temperature  ranges  and  for  the 
same  mixture  as  used  by  Clerk  by  the  aid  of  Mallard's  and  of 
Langen's  formulae.  This  involves  the  assumption  that  these 
formulas  hold  for  the  lower  temperature  ranges.  The  following 
table  shows  the  figures  so  obtained,  and  Fig.  10-4  gives  a  graphi- 
cal comparison. 

*  See  foot-note,  page  221. 


226 


INTERNAL  COMBUSTION  ENGINES 


MEAN  SPECIFIC  HEAT  FOR  MIXTURE  CONTAINING  BY  VOLUME  11.9  % 
H2O,  5.2  %  CO2,  7.9  %  O,  and  75  %  N. 


Temperature  Range 
°C                                  °F 

Mallard 
& 
Le  Chatelier 

Langen 

Clerk 

0-   100 

32-   212 

.1805 

.1826 

.1854 

0-  200 

32-   392 

.1843 

.1858 

.1910 

0-  400 

32-   752 

.1930 

.1922 

,2000 

0-   600 

32-1132 

.2006 

.1985 

.2083 

0-  800 

32-1472 

.2083 

.2047 

.2157 

0-1000 

32-1832 

.2161 

.2112 

.2202 

0-1200 

32-2192 

.2238 

.2176 

.2248 

0-1400 

32-2552 

.2315 

.2239 

.2284 

0-1500 

32-2732 

.2355 

.2271 

.2303 

0-150 
0-140 
0,130 

)°C 

/ 

/ 

/ 

'/ 

/ 

\ 

ariat 
f-a-A 

OI1S  ( 

ixtu 

I'M  i 
re-ro 
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7.-I.O 

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0-50(1 
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0-200 

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7 

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9 

lines 
.2 

o,C. 

.: 

\ 

! 

.1 

FIG.  10-4. 

It  is  .plain  from  Fig.  10-4  that  the  question  of  the  variation  of 
specific  heat  with  temperature  cannot  be  considered  entirely 
solved.  It  is  true  that  Stevens  *  made  experiments  on  air  which 
check  the  results  of  both  Mallard  and  Le  Chatelier  and  of  Langen 

*  Ann.  d.  Phys.,  1902. 


THE  FUEL  MIXTURE  227 

very  closely.  It  is  therefore  fair  to  assume  that  the  formulae 
derived  for  diatomic  gases  are  correct.  The  discrepancies  ob- 
served between  the  results  plotted  in  Fig.  10-4  are  therefore  with 
strong  probability  due  to  error  in  the  available  data  for  H2O  and 
CO2.  Further  work  is  therefore  required,  and  a  check  of  Clerk's 
results  is  especially  desirable. 

3.  Velocity  of  Flame  Propagation  and  Time  of  Explo- 
sion. —  Experiments  on  the  velocity  of  flame  propagation  in  a 
given  mixture,  like  the  experiments  on  specific  heat,  have  not  led 
to  any  definite  result.  And  although  definite  information  on 
this  point  is  desirable,  on  account  of  the  connection  between 
velocity  of  flame  propagation  and  possible  maximum  engine  speed, 
in  any  given  case  there  are  so  many  factors  affecting  the  problem 
in  actual  practice,  that  the  application  of  the  results  of  laboratory 
experiments  to  actual  conditions  is  of  doubtful  value.  Thus  the 
velocity  with  which  the  flame  spreads  through  a  mixture  depends 
upon  the  kind  of  fuel,  the  composition  and  purity  of  the  mixture, 
its  temperature  and  pressure,  and  upon  the  location  of  the  igniter 
and  the  shape  of  the  combustion  chamber.  Further  than  this,  the 
degree  of  mechanical  agitation  in  the  mixture  at  the  moment  of 
explosion  has  a  marked  influence  upon  the  velocity. 

If  we  ignite  a  mixture  in  a  tube,  closed  at  one  end,  from  the 
closed  end,  the  pressure  generated  seems  to  project  the  flame 
ahead  of  the  pressure  wave  toward  the  open  end  of  the  tube  with 
a  much  higher  flame  velocity  than  would  have  been  observed  if 
the  ignition  had  taken  place  from  the  open  end.  The  same  effect 
should  be  observed  in  a  tube  closed  at  both  ends.  Ignition  from 
the  open  end  gives  the  true  velocity,  as  the  flame  then  spreads  by 
contact  only.  In  an  actual  engine  cylinder,  with  the  volume  in- 
creasing with  the  movement  of  the  piston,  we  may  expect  the 
velocity  of  propagation  to  be  somewhere  between  those  found 
for  ignition  from  the  open  end  of  a  tube  and  those  for  ignition 
in  a  closed  tube. 

Mallard  and  Le  Chatelier  used  the  open-tube  method,  measur- 
ing the  time  interval  between  the  passage  of  the  pressure  wave 
between  two  points  on  the  tube.  Their  results,  as  given  by  Clerk, 
for  hydrogen  were  as  follows: 


228 


INTERNAL  COMBUSTION  ENGINES 


Mixture 

Velocity  of  Pressure 
Propagation 
ft.  per  second 

1  vol  H  -f-  4  vols  air 

6  56 

1  vol  H  +  3  vols  air                          

9  20 

1  vol  H  +  2J  vols  air                                   

11   10 

1  vol   H  -f-  1  f  vols  air 

12  40 

1  vol  H  +  l|  vols  air                  

14  30 

1  vol  H  -(-  1  vol  air                                      .      

12  30 

1  vol  H  +  ^  vol  air 

7  55 

The  true  explosive  mixture  for  hydrogen  and  air  is  1  vol.  of 
H  to  2£  vols.  of  air.  It  might  be  supposed  that  this  would  be 
the  mixture  showing  highest  velocity  of  propagation.  For  some 
unexplained  reason  a  certain  excess  of  hydrogen  shows  the  highest 


51)01 


-300- 


osed  e 


0         2         3         4          5         6         7          b         9         10        11        12       13 
Ratio  Air  to  Gas  by  Vol. 

FIG.  10-5. 

result.     A  similar  phenomenon  was  observed  with  coal  gas  and  air 
mixtures  by  these  observers. 

Meyer  *  used  an  apparatus  very  similar  to  that  of  Mallard  and 
Le  Chatelier,  except  that  very  sensitive  platinum  thermometers 
were  employed  to  measure  the  passage  of  the  flame,  instead  of 
diaphragms  to  measure  the  passage  of  the  pressure  wave.  The 
fuel  employed  was  coal  gas.  All  tests  were  made  with  the  mix- 
*  E.  J.  Meyer,  Sihley  College  thesis,  1905. 


THE  FUEL  MIXTURE 


229 


ture  at  atmospheric  pressure  at  the  time  of  ignition.  Figs.  10-5 
and  10-6  show  the  results  graphically,  the  former  being  obtained 
for  ignition  from  the  closed  end,  the  latter  for  ignition  from  the 
open  end.  The  much  higher  velocity  of  the  first  curve  bears  out 
the  statement  previously  made.  The  fact  that  the  maximum 
velocity  occurs  with  the  same  gas-air  ratio  shows  that  the  true 
rate  of  inflammability  has  not  been  changed,  but  that  mechanical 
actions  alone  are  responsible  for  the  difference  in  the  observed 
results. 

Closely  connected  with  the  velocity  of  flame  propagation,  and 
subject  to  the  influence  of  accidental  accompanying  conditions 
to  the  same  degree,  is  the  time  of  explosion.  The  most  extensive 
work  in  this  field  was  done  by  Clerk.  The  apparatus  employed 
by  him  was  very  similar  to  that  used  by  Langen  in  his  specific 


/ 

Vi 

,-er,  Ignition 

from 

•jO-fL^ 

/ 

\ 

opcr 

t  end 

x 
« 

°o  ° 

/ 

/ 

\ 

1 

Z 

/ 

Clerk, 

X 

Expl. 
l_v.ess< 

rtoG 

1 

g 

^-^^ 

0           1 

y 

Ei 

itio  A 

1Sbyj 

^v, 

.0,. 

^: 
i 

===^ 
n     i 

i 

2         1 

FIG.  10-6. 

heat  experiments.  The  fuel  mixture  was  ignited  at  constant 
volume  and  a  pressure  diagram  obtained  on  the  rotating  drum 
of  an  indicator.  Unfortunately  the  experiments  were  confined 
to  coal  gas,  a  few  figures  only  being  obtained  for  hydrogen  and. 
none  for  the  power  gases  so  important  to-day.  The  figures  found 
for  hydrogen  were  as  follows,  the  time  of  explosion  being  the  time 
interval  from  the  moment  of  ignition  to  the  attainment  of  maxi- 
mum pressure.* 


Mixture  by  Volume 

Time  of  Explosion 
in  seconds 

Air 

Hydrogen 

6 

1 

.150 

4 

1 

.026 

2.5 

1 

.010 

*  Clerk,  The  Gas  and  Oil  Engine,  p.  101. 


230 


INTERNAL  COMBUSTION  ENGINES 


Clerk's  results  for  mixtures  of  air  and  Oldham  coal  gas  are 
represented  in  Fig.  10-7.  The  volume  ration  showing  fastest 
time  of  explosion,  i.e.,  6  to  1,  agrees  with  the  mixture  for  which 
Meyer  found  the  greatest  velocity  of  flame  propagation.  This 
mixture  also  showed  about  the  highest  pressure  development  in 
Clerk's  experiments,  90  pounds  per  square  inch. 


—  — 

^ 

^~- 

^ 

^"^ 

/ 

/ 

> 

inn 

/ 

o 

/ 

Cle 

k,xi 
v 

ne  of  Expl. 
ssel,  (JHdliai 

n  closed 
iCoa/Gas. 

9  <i 

/ 



"o 

/ 

« 

\ 

'X 

^ 

-^^^ 

»       r 

f 

s      . 

2       .1 

0 

Tim 

0       .2 

;  in  Seconds 

4        .A 

•2       .3 

(»       .4 

1       .4 

-1        J 

8 

FIG.  10-7. 

In  Clerk's  experiments  the  pressure  at  the  moment  of  ignition 
was  atmospheric  in  each  case.  Koerting  *  carried  on  similar  ex- 
periments with  coal  gas  but  used  compressed  mixtures,  although 
the  pressures  used  were  low.  The  summary  of  his  results  is  as 
follows : 


Mixture  by  Vol. 

Pressure  before 
Ignition 
Lbs. 

Time  of  Explo- 
sion seconds 

Velocity  of  Propa- 
gation ft.  per  sec. 

Air 

Gas 

7.5 

1 

(  15.0 
(37.0 

.032 
.036 

23.0 
20.4 

5.42 

1 

(15 
137 

.01 
.0125 

74.0 
59.0 

*  Koerting,  Zeitschrift  d.  V.  d.  I. 


THE  FUEL  MIXTURE  231 

This  table  shows  that  compressing  the  mixture  retards  the 
velocity  of  flame  propagation,  but  that  the  amount  of  retardation 
is  less  in  lean  than  in  rich  mixtures  of  the  same  fuel. 

Koerting's  figures  do  not  agree  well  with  those  of  Clerk, 
although  they  were  obtained  with  similar  apparatus.  From  Fig. 
10-7  the  time  of  explosion  of  a  7.5  to  1  mixture  would  have  been 
about  .056  seconds  according  to  Clerk,  as  against  .032  seconds 
found  by  Koerting.  This  is  too  great  a  difference  even  assuming 
a  considerable  difference  in  the  composition  of  the  fuel.  The 
length  of  Clerk's  vessel  up  to  the  indicator  piston  was  about  10 
inches,  which,  with  a  time  explosion  of  .056  seconds,  gives  a 
velocity  of  propagation  in  a  closed  vessel  of  14.8  feet  per  second 
as  against  23  feet  found  by  Koerting. 

For  the  purpose  of  comparing  Clerk's  results  with  those  of 
Meyer  on  flame  propagation,  the  times  of  explosion  as  shown  by 
Fig.  10-7  have  been  transposed  to  the  basis  of  velocity  in  feet  per 
second.  The  resulting  curve  has  been  drawn  in  on  Fig.  10-5  with 
Meyer's  results.  It  is  seen  that  the  velocity  of  propagation  in  a 
closed  tube  according  to  Clerk  is  lower  than  that  found  by  Meyer 
for  ignition  from  the  open  end  of  a  tube,  except  for  ratios  exceed- 
ing 8  to  1,  and  here  the  difference  is  inconsiderable.  This  is  con- 
trary to  what  might  be  expected,  because,  as  before  explained, 
and  also  mentioned  by  Clerk,  if  explosion  takes  place  at  constant 
volume  in  a  closed  vessel,  the  part  of  the  mixture  first  ignited 
instantly  expands  and  shoots  the  flame  into  the  rest'  of  the  mass, 
thus  increasing  the  velocity  of  propagation.  As  compared  with 
Meyer's  results  for  ignition  from  the  closed  end  of  a  tube,  Clerk's 
results  are  very  much  lower,  in  fact  only  about  -£$  at  the  best  ratio 
for  the  gas.  Koerting's  figures,  on  the  other  hand,  slightly  exceed 
Meyer's  results  for  ignition  from  the  open  end. 


CHAPTER   XI 

HISTORICAL    SKETCH    OF    THE    INTERNAL    COMBUSTION    ENGINE 

1.  Origin  obscure.  —  The  origin  of  the  internal  combustion 
engine  is  imperfectly  known;  as  it  exists  at  the  present  time  it  is 
the  result   of  a  long-continued   development   which   began  first 
with  a  period  of  speculation  which,  through  the  efforts  of  numer- 
ous inventors,  finally  resulted  in  a  practical,  operative  machine. 
No  single  person  can  be  considered  as  the  inventor  of  the  internal 
combustion   engine.     Its   history   shows   the   existence   of  three 
periods:   (1)  that  of  speculation  and  invention;   (2)  that  of  de- 
velopment, and  (3)  that  of  application. 

2.  The    Period    of    Speculation    and  Invention.  —  The    gas 
engine  previous  to  1860  was  not  a  practical,  commercial  machine 
nor  had  it  been  used  to  any  great  extent  "for  the  purposes  of 
producing   power.     Previous   to   that   time   various   publications 
arid   patents  show  that   nearly   all   of  the  types  known    at    the 
present  time  had  been  discovered,  although  the  records  are  im- 
perfect as  to  the  actual  and  practical  use  of  such  machines.     It 
is  reasonable  to  believe  that   many  of  the  forms  described  or 
patented  were  actually  built  and  operated  experimentally  if  not 
commercially. 

Aime  Witz  gives  the  credit  *  for  the  first  internal  combustion 
engine  to  the  Abbe  Hautefeuille,  who  describes  an  engine  in  1678 
in  which  water  is  raised  by  utilizing  the  partial  vacuum  which 
results  from  burning  gunpowder  in  a  cylinder  and  cooling  the 
gases  remaining. 

A  similar  engine  was  described  by  Huygens  in  a  memoir  en- 
titled "  Une  nouvelle  force  mouvant  par  le  moyen  de  la  poudre  a 
canon  et  de  Pair,"  which  appeared  in  1680.  Denis  Papin  con- 
structed an  internal  combustion  engine  similar  to  that  described 
by  Huygens  in  1690,  but  on  account  of  imperfect  workmanship 

*  Moteurs  a  Gaz  et  a  Petrole. 
232 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      233 

obtained  results  very  much  inferior  to  those  produced  by  a  steam 
engine  and  abandoned  the  powder  engine  as  an  impractical 
machine. 

In  the  powder  engines  the  method  was  a  fairly  practical  one; 
a  small  quantity  of  gunpowder  exploded  in  a  large  cylindrical 
vessel  expelled  the  air  through  check  valves,  thus  leaving,  after 
cooling,  a  partial  vacuum  below  the  piston.  The  pressure  of  the 
atmosphere  did  work  by  moving  the  piston  downward. 

For  a  long  time  after  this  attempt,  the  internal  combustion 
engine  seemed  to  have  been  practically  forgotten,  as  the  next 
description  of  its  construction  was  not  written  until  after  Watt 
had  developed  and  improved  the  steam  engine.  Considering  the 
low  condition  of  the  state  of  the  mechanical  arts  and  the  diffi- 
culty of  obtaining  good  workmen  and  proper  materials,  which 
Watt  experienced  and  which  he  was  only  able  to  overcome  by 
spending  years  of  time,  it  can  be  readily  understood  why  little 
or  no  substantial  progress  was  made.  Watt  not  only  solved  the 
problem  relating  to  the  method  of  improving  the  engine,  but  he 
also  developed  in  a  very  great  measure  the  art  of  constructing  such 
engines  and  of  producing  proper  materials  for  their  manufacture. 

The  greater  portion  of  the  information  relating  to  the  design 
and  improvement  of  the  gas  engine  during  the  period  previous 
to  any  extensive  commercial  use  is  obtained  from  the  records  of 
the  English,  French  and  American  patent  offices.  These  records 
have  the  advantage  over  other  publications  of  being  definitely 
dated  and  of  concisely  and  accurately  describing  the  machine 
and  its  mode  of  operation. 

The  first  internal  combustion  engine  described  in  the  patent 
records  was  patented  by  Robert  Street  in  England  on  the  7th 
of  May,  1794.  It  consists  of  a  motor  cylinder,  with  a  piston,  the 
bottom  of  which  is  heated  by  fire.  The  patent  shows  a  pump 
driven  by  a  lever.  The  fuel  is  described  as  a  small  quantity  of 
tar  or  turpentine  which  is  projected  onto  the  hot  part  of  the 
cylinder  so  that  the  liquid  is  instantly  converted  into  an  inflam- 
mable vapor.  The  raising  of  the  piston  by  means  of  a  lever  sucks 
in  external  air  and  also  flame  for  ignition,  which  causes  the  ex- 
plosion. The  details  as  described  are  crude,  but  the  principle  of 
operation  is  the  same  as  in  the  Lenoir  engine  which  was  patented 
in  1860. 


234 


INTERNAL  COMBUSTION  ENGINES 


Phillippe  Lebon  patented  in  France,  in  1801,  a  gas  motor  in 
which  the  gas  was  compressed  in  a  cylinder  external  to  the  work- 
ing cylinder  previous  to  ignition.  In  this  patent  there  is  de- 
scribed the  use  of  an  air  pump  for  compressing  atmospheric  air,  • 
a  gas  pump  for  compressing  gas,  and  the  use  of  electricity  for 
ignition.  Lebon  died  September  22,  1804.  Witz  states  "that  it 
is  probable  that  the  industry  of  building  gas  engines  would  have 
dated  at  the  beginning  of.  the  century  as  a  practical  commercial 
industry,  instead  of  1860,  had  he  lived." 

Various  inventors  early  in  the  century  proposed  the  use  of 

explosive  powders,  of  air  satu- 
rated with  hydrocarbon  and 
of  hydrogen  gas  produced  by 
chemical  means,  as  fuels  for  in- 
ternal combustion  engines,  but 
these  did  not,  so  far  as  can  be 
ascertained,  result  in  any  prac- 
tical improvement. 

In  1823  and  1826  Samuel 
Brown  obtained  English  patents 
for  an  ingenious  atmospheric 
air  engine  which,  although  very 
cumbersome  and  uneconomical, 
was  applied  to  practical  uses. 
The  engine,  Fig.  11-1,  was  oper- 
ated by  burning  the  combusti- 
ble in  a  vessel  adjacent  to  the 
working  cylinder,  which  resulted  in  expelling  a  portion  of 
the  air  it  contained.  A  jet  of  water  was  then  thrown  in 
which  lowered  the  temperature  and  by  so  doing  produced  a 
vacuum.  Motion  was  produced  by  the  atmospheric  pressure 
acting  alternately  on  the  sides  of  the  piston  in  the  working 
cylinder,  which  was  arranged  adjacent  to  the  vacuum-produc- 
ing chamber  and  put  in  alternate  connection  with  it  by  means 
of  a  proper  valve  motion.  This  engine,  although  referred  to  by 
Clerk  "as  being  the  first  gas  engine  undoubtedly  put  at  work," 
is  an  external  combustion  gas  engine  somewhat  similar  to  the 
Wilcox  engine  already  described,  except  that  there  was  vacuum 
rather  than  pressure  in  the  combustion  vessel.  According  to  the 


FIG.  11-1.  — S.  Brown,  1823-26. 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      235 


Mechanics  Magazine,  published  in  London,  a  boat  was  fitted  with 
a  Brown  engine  and  ran  experimentally  upon  the  Thames. 
Another  engine  was  made  in  combination  with  a  road  carriage 
(see  Mechanics  Magazine,  December  24,  1825);  this  is  also 
referred  to  in  a  Report  of  a  Committee  of  the  House  of  Com- 
mons, reprinted  as  a  public  document  in  the  United  States  in  1832. 

W.  L.  Wright  obtained  an  English  patent  (No.  6525  of  1833) 
for  an  internal  combustion  engine  in  England.  This  patent  is 
accompanied  with  elaborate  drawings  giving  in  detail  the  pro- 
posed construction.  The  engine,  Fig.  11-2,  is  shown  as  double 
acting,  the  piston  receiving  two  im- 
pulses for  every  revolution  of  the 
crank  shaft.  It  is  also  shown  as  pro- 
vided with  pumps  adapted  to  com- 
press the  air  and  gas  a  few  pounds 
above  the  atmosphere  previous  to 
their  introduction  into  the  cylinder. 
The  engine  was  provided  with  a  fly- 
ball  governor  for  controlling  the  quan- 
tity of  gas  and  air  as  required  to 
produce  uniform  speed.  The  charge 
is  ignited  when  the  working  piston  is 
at  the  end  of  its  stroke  by  an  external 
flame,  burning  in  air,  which  is  con- 
nected with  the  charge  at  the  proper 
time  by  a  valve  opened  by  the  mech- 
anism of  the  engine.  The  charge 
was  not  under  sensible  compression 

at  the  time  of  ignition.  The  engine  as  shown  has  water-jacketed 
cylinder  and  piston,  poppet  exhaust  valves  operated  by  cams, 
and  appears  well  proportioned  throughout.  Much  credit  is  due 
to  the  governing  device  shown,  and  it  would  be  difficult  to  state 
why  the  motor  did  not  succeed,  unless  it  may  have  been  due  to 
the  lack  of  demand  for  any  other  motor  than  the  steam  engine. 

James  Johnson  took  out  an  English  patent  in  1841  for  a  gas 
engine  to  be  operated  by  hydrogen  gas.  In  this  engine  the  piston 
is  forced  to  the  end  of  the  cylinder  by  the  explosion  of  the  gas, 
after  which  a  vacuum  is  formed  underneath  the  piston  and  the 
piston  is  returned  by  atmospheric  pressure.  It .  illustrates  the 


FIG.  11-2.  — Wright,  1833. 


236 


INTERNAL  COMBUSTION  ENGINES 


expansion  of  the  products  of  combustion  below  atmospheric 
pressure,  a  method  which  as  yet  has  not  met  with  much  practi- 
cal success  in  the  operation  of  gas  engines. 

William  Barnett  obtained  a  patent  in  England  (No.  6015,  of 
1838),  which  describes  the  construction  and  mode  of  operation 
of  a  two-cycle  gas  engine,  single  and  double  acting,  in  which  the 
explosive  mixture  is  compressed  previous  to  ignition.  It  shows 
three  forms  of  engines,  one  type  in  which  the  compression  is 
entirely  performed  outside  the  working  cylinder  and  which  is 
shown  as  both  single  and  double  acting.  It  also  shows  another 

type  in  which  the  compression  is  com- 
pleted inside  the  working  cylinder, 
this  latter  form  being  almost  identical 
with  the  modern  two-stroke  cycle  en- 
gine which  has  already  been  described. 
Barnett  also  shows  an  igniting 
device,  described  in  Chapter  XIII, 
which  is  adapted  to  ignite  the  gase- 
ous mixture  while  under  compression. 
This  met  hod.  of  ignition  is  of  interest 
as  it  was  used  in  a  slightly  different 
form  by  Otto  in  the  Otto  engine  in 
1877.  Barnett  also  describes  a  method 
of  igniting  by  bringing  the  explosive 
mixture  in  contact  with  spongy  plati- 
num which  is  located  in  a  cavity  near 
the  head  of  the  cylinder. 
Figure  11-3  is  reduced  from  patent  drawing  and  shows  a 
section  of  the  single-acting  engine  in  which  A  is  the  motor  piston. 
The  cylinder  is  open  at  the  top,  B  is  a  double-acting  pump  which 
serves  to  supply  atmospheric  air  to  form  an  explosive  mixture 
on  one  side  and  to  exhaust  the  products  of  combustion  on  the 
other;  the  pump  for  supplying  fuel  gas  under  compression  stands 
back  of  the  air  pump  and  is  not  shown  in  the  figure.  During  the 
ascent  of  the  piston,  A,  the  air  and  gas  pumps  have  been  drawing 
in  air  and  gas,  which  on  the  descent  of  the  pump  pistons  are 
forced  into  the  receiver,  D,  which  is  separated  from  the  working 
cylinder  by  the  piston  slide  valve,  E.  In  the  meantime  the  pis- 
ton A  has  discharged  the  exhaust  gases  through  the  valve  E. 


FIG.  11-3.  —  Barnett,  1838. 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      237 


This  valve  closes  communication  with  the  air  when  A  reaches 
the  lower  dead  center  and  opens  communication  with  the  re- 
ceiver D.  At  this  instant  the  charge  is  ighited,  and  the  gases 
under  compression  pass  into  the  working  cylinder  through  the 
slide  valve  E.  The  igniting  device  shown  at  F  is  operated  by 
the  motion  of  the  valve. 

The  gases  at  the  time  of  explosion  are  in  the  receiver  D,  and 
flow  through  the  port  after  ignition  precisely  as  steam  would  do. 
The  pressure  in  the  motor  cylinder 
falls  by  expansion  with  increase  in 
volume  due  to  motion  of  piston. 

Barnett's  second  engine  is  identi- 
cal with  his  'first  except  that  it  is 
double  acting. 

Barnett's  third  engine,  shown  in 
Fig.  11-4,  is  of  great  interest  since  it 
is  the  forerunner  of  the  modern  two- 
cycle  engine.  The  engine  shown  in 
the  figure  is  double  acting.  Like  the 
first  engine  it  has  three  cylinders, 
motor  cylinder  A,  air  pump  B,  and 
a  gas  pump  not  visible  in  the  figure. 
The  air  and  gas  pumps  are  single 
acting  but  are  operated  by  means  of 

gearing  so  as  to  make  twice  as  many  FJG  n_4  _  Bamett,s  Third 
strokes  as  the  working  piston.  The  Engine. 

ignition  is  performed  by  spongy  plati- 
num with  which  the  gases  under  compression  are  brought  in 
contact.  The  operation  of  the  engine  is  as  follows,  supposing 
that  when  the  piston  is  in  the  position  shown  in  the  draw- 
ing it  is  moving  upward  and  the  upper  end  of  the  cylinder 
is  charged  with  air  and  gas  under  compression.  When  the 
piston  has  completed  its  up  stroke,  the  contact  of  the  plati- 
num with  the  compressed  mixture,  produced  by  the  ascent  of 
the  piston,  causes  explosion,  which  in  turn  impels  the  piston 
to  the  bottom  of  its  stroke.  During  the  first  part  of  the 
descent  and  until  the  piston  passes  the  port,  M,  at  the  center  of 
the  cylinder,  the  products  of  combustion  below  the  piston  are 
being  exhausted,  either  into  the  atmospheric  air  or  into  an 


238 


INTERNAL  COMBUSTION  ENGINES 


exhaust  pump,  which  may  be  used  if  desired.  At  the  same  time 
the  air  and  gas  pumps  draw  in  their  respective  charges.  During 
the  latter  half  of  the  descent  of  the  piston  the  air  and  gas  pumps 
are  forcing  the  mixed  air  and  gas  into  the  cylinder  below  the 
piston  where  it  is  further  compressed  and  exploded  at  the  end 
of  its  stroke,  in  which  case  the  piston  is  forced  upwards  and  the 
operation  is  repeated. 

Stuart  Perry  patented  in  the  United  States,  May  25,  1844, 
and  in  Great  Britain  through  the  agency  of  Joseph  Robinson 
(No.  9972  of  1843),  a  gas  or  vapor  engine 
which  was  provided  with  means  for  compress- 
ing the  charge  previous  to  ignition.  The 
method  of  ignition  in  the  Perry  engine  was 
similar  to  that  in  the  Wright  engine.  The 
engine  was  especially  designed  for  the  use  of 
iKfbiid  hydrocarbon,  and  for  this  purpose  it 
was  provided  with  a  carbureter  through  which 
a  portion  of  the  air  on  its  way  to  the  engine 
is  forced  and  which  may  be  heated  by  the 
exhaust  gases.  The  Perry  engine  is  double 
acting  and  provided  with  a  rotating  valve 
which  by  means  of  gearing  can  be  reversed 
in  direction,  thus  reversing  the  engine. 

The  Perry  patent  of  1844  was  followed 
by  one  in  1846  which  showed  an  engine  with 
poppet  valves  and  with  means  for  igniting  by 
a  hot  tube  consisting  of  a  platinum  cup  kept 
hot  by  a  gas  flame.  In  this  latter  engine  the 
charge  was  under  compression  at  the  time  of  ignition.  In  the 
latter  patent  reference  is  made  to  the  actual  use  of  a  gas  engine 
with  carbureting  device,  from  which  it  would  appear  that  Perry 
at  least  anticipated  in  design  many  later  constructions. 

A.  V.  Newton  obtained  a  patent  in  England  (No.  562  of  1855), 
for  an  ignition  device  which  was  identical  with  that  formerly 
patented  in  America  by  Drake,  and  which  is  now  known  as  the 
hot-tube  method  of  ignition.  The  igniting  arrangement  consists 
of  a  cast-iron  tube,  closed  at  the  outer  end,  which  projects  into 
a  recess  formed  in  the  side  of  the  cylinder.  A  gas  flame,  Fig. 
11-5,  keeps  a  section  of  this  tube  at  a  temperature  sufficient  to 


FIG.  11-5.  - 

Newton's  Hot  Tube 

Igniter. 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      239 


explode  the  charge  when  the  piston  uncovers  the  opening.  The 
engine  shown  in  the  Newton  patent  is  a  non-compression  double- 
acting  engine  with  water  jackets. 

Barsanti  and  Matteucci  of  Florence,  Italy,  took  an  English 
patent  (No.  1655  of  1857)  for  a  free  piston  vacuum  engine,  which 
is  of  interest  from  the  fact  that  it  was  of  essentially  the  same  class 
as  a  successful  type  of  engine  which  was  introduced  some  years 
later  by  Otto  and  Langen.  In  this  engine  the  force  of  the  ex- 
plosion was  utilized  in  moving  the  piston  when  free  from  the 
connecting  rod,  the  work  being  done  on  the 
return  stroke  by  the  weight  of  the  piston  and 
by  atmospheric  pressure  acting  on  its  upper 
side. 

In  construction  the  cylinder  of  the  engine 
is  vertical,  open  at  the  top  and  very  long, 
Fig.  11-6.  The  charge  consisting  of  gas 
and  air  enters  when  the  piston  is  drawn  up 
a  short  distance  and  is  exploded  by  an  elec- 
tric spark.  The  piston  rod  carries  a  rack 
which  is  in  engagement  with  a  gear  wheel 
connected  by  a  ratchet  and  pawl  to  the  main 
shaft.  When  the  piston  is  shot  rapidly  up- 
ward the  gear  wheel  turns  without  moving 
the  main  shaft.  When  the  piston  returns 
the  ratchet  connects  the  gear  wheel  of  the 
main  shaft  so  that  it  is  turned  in  the  direc- 
tion for  producing  work. 

Clerk  states  that  the  method  illustrated 

in  this  engine  possesses  three  advantages:  rapid  expansion,  a 
large  amount  of  expansion,  and  also  some  of  the  advantages  of 
a  condenser. 

3.  Period  of  Development.  —  LP:NOIR.  The  first  internal 
combustion  engine  to  attain  any  marked  degree  of  commercial 
success  was  patented  by  J.  J.  E.  Lenoir,  in  France,  January  4, 
1860,  and  in  the  United  States  March  19,  1861. 

The  Lenoir  engine  was  of  simple  construction  and  belonged 
to  a  type  which  had  been  previously  described  by  several  inven- 
tors. Its  success  was  evidently  due  to  the  good  proportions 
which  characterized  the  design.  The  engine  cylinder  is  shown 


FIG.  11-6.  —  Barsanti 
and  Matteucci. 


240 


INTERNAL  COMBUSTION  ENGINES 


in  section  in  Figs.  11-7  and  11-8.  This  engine  belongs  to  the 
class  in  which  the,  ignition  takes  places  while  the  charge  has 
practically  constant  volume  and,  in  the  case  of  the  Lenoir  engine, 


FIG.  11-7.  —  Lenoir  Engine,  1860, 

had  not  been  compressed  previous  to  ignition;  it  is  devoid  of  any 
compression  mechanism.  In  structure  it  resembles  that  of  a 
double-acting  steam  engine  with  separate  slide  valves  for  the 


FIG.  11-8.  —  Lenoir  Engine,  1860. 

admission  and  exhaust.  Thus  in  Fig.  11-7  the  charge  is  ad- 
mitted by  the  slide  valve  G,  and  is  exhausted  by  the  slide 
valve  H.  It  is  drawn  into  the  cylinder  by  the  partial  vacuum 
produced  by  the  motion  of  the  piston,  the  slide  valve  being 
arranged  to  open  the  ports  at  the  beginning  of  the  stroke  and 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      241 

close  them  at  about  the  center  of  the  stroke.  The  charge  is 
exploded  by  electrical  means  when  the  piston  is  at  about  the 
middle  of  its  stroke,  and  produces  the  requisite  pressure  to  force 
the  piston  onward  and  keep  the  engine  in  motion.  The  exhaust 
valve  opens  to  discharge  the  products  of  combustion  during  the 
return  stroke.  The  operation  of  both  ends  of  the  engine  takes 
place  alternately  and  tends  to  produce  a  uniform  motion  of  the 
fly-wheel. 

The  engine  is  shown  provided  with  cross-head,  connecting  rod, 
and  governor  similar  to  a  steam  engine.  The  governor  is  arranged 
to  throttle  the  supply  of  gas  as  required  to  produce  uniform 
speed.  The  engine  was  provided  with  a  device  for  timing  the 
electrical  spark.  The  source  of  electricity  was  a  primary  battery 
arranged  to  intensify  the  current  by  an  induction  coil. 

Although  the  consumption  of  gas  by  this  engine  was  always 
high  and  the  power  produced  in  porportion  to  the  cylinder  very 
small,  yet  it  possessed  certain  advantages.  Its  mechanism  is 
simple,  its  explosion  nearly  without  shock,  and  its  action  very 
smooth.  This  .engine  was  sold  in  large  numbers  and  manufac- 
tured both  in  France  and  England. 

Dugald  Clerk  quotes  from  an  article  in  the  Practical  Mechanics 
Journal  of  August,  1865,  showing  that  from  300  to  400  engines 
were  at  that  time  at  work  in  France.  He  also  states  that  the 
Reading  Iron  Works  Co.,  at  Reading,  England,  made  and  delivered 
100  engines. 

Witz  states  that  this  engine  was  received  with  great  enthu- 
siasm and  that  many  predicted  that  the  last  hours  of  the  steam 
engine  had  sounded  and  that  the  star  of  Watt  paled  before  that 
of  Lenoir.  This  enthusiasm  resulted  in  a  marked  exaggeration 
both  as  to  economy  and  capacity,  which  was  followed  by  a  re- 
action during  which  time  the  engine  was  called  a  humbug  and 
many  were  broken  up  for  old  iron.  It  was,  however,  appreciated 
at  its  full  value  at  a  later  time,  as  it  was  found  extremely  well 
adapted  for  small  establishments  requiring  from  £  horse-power 
to  4  horse-power.  For  such  uses  the  consumption  of  gas  was 
guaranteed  to  be  less  than  70  cu.  ft.  per  horse-power  hour  and  this 
guarantee  seems  to  have  been  usually  realized.  Juries  at  the 
expositions  of  London  in  1862,  of  Paris  in  1867,  of  Vienna  in  1873, 
recognized  the  merit  of  Lenoir. 


242  INTERNAL  COMBUSTION  ENGINES 

The  Lenoir  engine  is  described  as  adapted  to  be  operated 
either  with  gas  or  with  the  vapor  of  liquid  hydrocarbon,  and  in  a 
French  patent  of  1861  a  carbureter  is  shown  for  mixing  the  vapor 
of  oil  with  air. 

The  engine  of  Lenoir  was  used  for  various  purposes,  for  in- 
stance, printing,  pumping  water,  driving  lathes,  and  also  for  the 
purpose  of  propelling  a  vehicle  and  a  road  carriage. 

In  the  report  of  the  Vienna  Exhibition  of  1873,  R.  H.  Thurston 
quotes  the  following  statements  of  M.  Claudel  in  reference  to  the 
experiments  of  M.  Tresca  on  the  Lenoir  engine : 
"The  speed  of  the  engine  is  variable." 
"The  failure  to  ignite  a  single  charge  will  stop  it." 
"To  start  it  it  is  necessary  to  give  it  several  revolutions  by 
hand." 


Speed,  50  rev '-per  mm. 


FIG.  11—9.  —  Diagram  Lenoir  Engine. 

"  Lubricant  must  be  abundant'  and  the  amount  of  oil  cannot 
be  estimated  at  less  than  0.5  kilogram  (1.1  Ibs.)  per  day." 

"To  obtain  the  best  effect,  it  is  necessary  to  open  the  inlet 
before  the  complete  closing  of  the  exhaust  valve." 

"  A  machine  of  0.24  meter  (9.5  inches)  diameter  of  cylinder  pro- 
duced very  nearly  one  horse-power." 

The  best  performance  claimed  for  the  Lenoir  engines  is  70  to 
74  cu.  ft.  of  gas  per  horse-power  per  hour.  M.  Tresca  reported  a 
consumption  of  95.28  cu.  ft.  A  typical  indicator  diagram  from  a 
Lenoir  engine  is  shown  in  Fig.  11-9. 

HUGON.  —  It  has  been  shown  that  Hugon  had  experimented 
with  an  engine  of  the  Lenoir  type  two  years  before  Lenoir.*  But 
while  the  obvious  disadvantages  of  the  construction  did  not  pre- 
vent Lenoir  from  putting  his  engine  on  the  market,  Hugon  was 
not  satisfied  with  the  solution  of  the  problem  and  turned  his 
attention  to  the  indirect  acting  engine  of  the  type  of  Barsanti 

*  Memoirs  des  Ingenieurs  Civils,  1860,  p.  159. 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      243 

and  Matteucci.  Only  after  the  Lenoir  engine  proved  in  a  certain 
manner  a  commercial  success  did  Hugon  return  to  his  former 
engine,  and,  making  some  improvements  on  Lenoir,  brought  the 
engine  out  in  1864.  In  this  machine,  Figs.  11-10  and  11-11, 
electric  ignition  was  replaced  by  flame  ignition,  which  was  much 
the  surer  method  of  igniting  a  charge  in  those  early  days,  and 


FIG.  11-10.  —  Cylinder,  Hugon  Engine,  1864. 

both  exhaust  and  inlet  were  operated  by  one  valve  in  order  to  give 
this  valve  the  advantage  of  cooling  by  the  incoming  cold  mixture. 
To  overcome  the  very  serious  defect  of  the  Lenoir  engine  existing 
in  the  extremely  rapid  wear  of  the  valves,  Hugon  reduced  the 
temperatures  of  the  cycle  by  injecting  water  into  the  charge. 
The  Hugon  engine  was  somewhat  superior  to  that  of  Lenoir 


FIG.  11—11.  —  Hugon 's  Flame  Ignition  Valve. 

in  both  fuel  and  lubricating  oil  consumption,  but  it  did  not  find 
the  degree  of  application  of  the  latter,  because  apparently  the 
means  were  not  at  hand  to  exploit  it  to  the  extent  done  with  the 
Lenoir  machine. 

BEAU  DE  ROCHAS,  1862.  —  In  a  patent  taken  out  in  Paris  by 
Alph.  Beau  de  Rochas  on  January  7,  1862,  he  states  the  conditions 
required  for  the  highest  efficiency  in  an  internal  combustion 


244  INTERNAL  COMBUSTION  ENGINES 

engine,  and  he  also  distinctly  describes  the  working  cycle  which 
in  his  opinion  is  necessary  to  produce  the  highest  efficiency. 

According  to  this  investigator,  the  conditions  necessary  for 
highest  efficiency  are  four  in  number:  (1)  the  greatest  volume 
of  the  cylinder  possible  having  a  minimum  surface  of  periphery; 
(2)  highest  possible  velocity  of  motion;  (3)  greatest  possible 
expansion;  (4)  greatest  possible  pressure  at  the  commencement 
of  the  expansion.  He  states  that  for  highest  efficiency  it  is 
necessary  to  execute  the  following  operations  in  the  period  of 
four  consecutive  strokes  in  each  end  of  the  cylinder. 

(1)  Aspiration  during  an  entire  out  stroke  of  the  piston. 

(2)  Compression  during  the  following  in  stroke. 

(3)  Ignition  at  the  dead  point  and  expansion  during  the  third 
stroke. 

(4)  Discharge  of  the  burned  gases  from  the  cylinder  during 
the  fourth  and  last  stroke. 

The  operations  which  are  described  above  characterize  the 
four-stroke  cycle  engine  which  was  first  actually  built  by  Otto 
in  1876  or  1877.  The  importance  of  the  pamphlet  of  Beau  de 
Rochas  was  not  recognized  and  it  was  probably  little  read  until 
Otto  had  established  the  practical  value  of  this  method  of  opera- 
tion. Five  years  before  his  death  in  1887  Beau  de  Rochas  was 
given  a  prize  by  the  Societe  de  Encouragement  pour  1' Industrie 
Nationale  as  a  recognition  of  the  important  part  which  he  had 
played  in  the  development  of  the  internal  combustion  motor. 

Although  the  importance  of  compression  previous  to  ignition 
in  increasing  both  the  efficiency  and  capacity  of  the  internal 
combustion  engine  was  fully  pointed  out  by  Million  in  his  English 
and  American  patents  and  by  the  pamphlets  of  Beau  de  Rochas, 
little  or  no  practical  progress  was  made  in  the  construction  of 
compression  engines  for  the  next  twelve  years.  The  practical 
applications  were  confined  in  a  large  measure  to  the  production 
of  non-compression  engines  of  the  same  type  as  that  of  Lenoir. 

OTTO  AND  LANGEN.  —  Early  in  1861,  N.  A.  Otto,  in  trying 
to  improve  Lenoir's  engine  by  giving  it  a  full  power  stroke,  hit 
upon  the  idea,  in  the  course  of  his  investigations,  to  break  the 
igniter  circuit  of  one  of  these  machines,  keep  the  exhaust  valve 
closed  at  the  end  of  the  out  stroke,  then  to  turn  the  engine  back 
in  the  other  direction  by  hand,  and  when  the  piston  reached  the 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      245 


inner  dead  center,  having  compressed  the  charge,  to  cause  the 
spark  to  jump.  He  thus  half  unconsciously  reproduced  the  suc- 
tion and  compression  strokes  of  our  modern  four-cycle  engines, 
and  the  result  was  that  the  engine  received  a  sudden  impulse 
which  kept  it  spinning  for  several  revolutions.  As  near  as  Otto 
thus  came  to  the  solution  of  the  question,  as  proposed  by  Beau 
de  Rochas  in  1862,  practical  difficulties  encountered,  together 
with  his  own  failures  to  realize  the  full  importance  of  the  thing, 
caused  him  to  turn  aside  and  invent  an 
engine  of  an  entirely  different  type.  Not 
until  thirteen  or  fourteen  years  later  did 
he  return  to  the  old  problem  with  success. 

The  result  of  his  labor  in  the  early 
sixties  was  the  so-called  free  piston  en- 
gine. The  idea  had  been  already  worked 
out  by  Brown  in  1832  and  by  the  Italian 
Barsanti  in  1858,  but  it  remained  for 
Otto  and  Langen  to  make  it  a  commer- 
cial success. 

After  several  years  of  experimentation 
the  first  machine  was  exhibited  at  the 
Paris  Exposition  in  1867. 

Flame  ignition  was  used  and  much 
better  economy  was  obtained  than  with 
the  Lenoir  or  Hugon  engine.  Clerk  states 
that  "it  completely  crushed  Lenoir  and 
Hugon  and  held  almost  sole  command  of  the  market  for  ten 
years,  several  thousands  being  constructed  in  that  period." 

A  section  of  the  engine  is  shown  in  Fig.  11-12.  It  consists  of 
a  tall  vertical  cylinder  water-jacketed  through  a  part  or  the  whole 
of  its  length  writh  the  top  open  to  the  air.  The  fly-wheel  shaft  is 
supported  by  bearings  on  the  top  and  carries  a  gear  wrhich  engages 
with  a  rack  attached  to  the  piston  rod  of  the  engine.  The  gear 
turns  freely  on  the  shaft  while  the  piston  is  moving  upward,  but 
is  connected  with  it  by  an  ingenious  clutch  when  the  piston  moves 
downward.  A  slide  valve  S,  operated  by  an  eccentric  on  a  shaft 
geared  to  the  main  shaft,  controls  the  admission,  ignition,  and 
exhaust  intermittently  as  determined  by  the  governor  of  the 
engine.  When  operating  at  full  load  the  piston  is  lifted  a  few 


FIG.  11-12. —  Otto-Langen 
Free  Piston  Engine. 


246 


INTERNAL  COMBUSTION  ENGINES 


inches  and  takes  in  the  charge  through  the  slide  valve,  which  soon 
moves  further  and  brings  in  the  igniting  flame.  The  resulting 
explosion  projects  the  piston  upward  with  high  velocity.  The 
pressure  beneath  it  rapidly  falls  by  expansion  until  lower  than 
that  of  the  atmosphere.  On  the  return  stroke  of  the  piston  the 
clutch  is  in  engagement  with  the  shaft  and  performs  work  due  to 
the  weight  of  the  piston  falling  freely  into  a  partial  vacuum.  The 
exhaust  gases  in  the  meantime  are  displaced  through  a  port  in  the 
valve. 

The  clutch  of  the  Otto-Langen  engine  was  a  very  ingenious 
construction  and  one  of  the  main  points  of  the  invention.  It  is 
shown  in  detail  in  Fig.  11-13  and  consists  of  a  part  a  keyed  to 


FIG.  11-13.  — Clutches,  Otto-Langen  Engine. 

the  shaft,  on  which  runs  the  part  b  carrying  the  teeth  engaging 
the  rack.  The  part  a  revolves  freely  with  the  shaft  and  is  dis- 
connected from  the  part  b  while  the  piston  is  moving  upward 
or  is  stationary,  but  is  fastened  to  the  part  6  when  the  piston 
is  moving  downward.  The  parts  a  and  b  are  engaged  by  small 
rollers,  e,  moving  over  wedge-shaped  clips,  cc,  when  the  part  b 
moves  in  the  same  direction  as  the  part  a  and  at  a  higher  rate  of 
speed.  The  parts  are  clamped  together  by  the  rollers  wedging 
in  between  the  two  inclined  surfaces  and  the  steel  clips  cc.  It 
will  be  seen  that  as  soon  as  the  part  a  moves  with  a  higher  velocity 
than  is  imparted  to  b  by  the  rack,  the  clutch  releases  automati- 
cally. 

Dr.  R.  H.  Thurston,  in  the  report  of  the  Vienna  exhibition  in 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      247 


1873,  states  that  several  of  these  engines  were  on  exhibition  and 
the  results  of  several  series  of  tests  made  by  M.  Tresca  are  given. 
The  dimensions  of  the  engine  tested  were  as  follows:  diameter  of 
piston,  8.75";  maximum  stroke,  41.3";  diameter  of  water  jacket, 
15.75";  height  of  water  jacket,  28.0".  The  following  are  the  re- 
sults of  four  trials: 


Trials 

1 

2 

3 

4 

Pressure  of  gas,  millimeters  

30.5 

36 

36 

Duration  of  experiments,  *hrs  
Revolutions  per  min 

4 

85  7 

1 

82 

0.5 

81  5 

0.5 

79  9 

Brake  H   P 

0  896 

0  857 

0426 

0418 

Total  gas  per  hr.   litres 

1017  5 

1085 

560 

560 

Gas  per  H.  P.  hr.,  litres   

1135.6 

1266 

1314 

1339  7 

Gas  per  H.  P.  hr.,  cu.  ft  
Gas  used  for  igniters  per  hour,  cu.  ft. 

39.4 
2.12 

44 
2.30 

45.5 

46 

The  above  results,  however,  have  been  surpassed  in  tests  by 
Meidinger  in  1868.  The  engine  tested  had  a  cyl. -diameter 
of  5.9",  a  maximum  stroke  of  38.7",  and  was  rated  at  \  horse- 
power. At  maximum  load  this  engine  developed  .635  B.  H.  P. 
and  showed  a  gas  consumption,  including  that  of  the  ignition 
flame,  of  29.5  cu.  ft.  per  B.  H.  P.  hour.  This  corresponds  to  a 
thermal  efficiency  on  the  brake  of  13.7  per  cent.  Curiously  enough 
a  still  better  economy  was  shown  at  a  lower  load.  With  a  B.  H.  P. 
of  .35,  the  efficiency  was  15.4  per  cent.  The  fuel  mixture  in  both 
cases  contains  12.5  per  cent  of  gas. 

Respecting  the  engine  tested  at  Vienna,  Dr.  Thurston  states 
that  it  has  always  worked  well  and  has  greatly  reduced  the  con- 
sumption of  gas  over  that  used  by  earlier  engines.  It  is  very  noisy 
in  operation  and  the  exceptional  fuel  economy  is  its  only  special 
recommendation.  This  economy  is  probably  due  principally  to  the 
extreme  rapidity  with  which  the  piston  is  projected  upward  at 
each  explosion  of  gas,  the  work  of  expansion  being  thus  utilized 
before  sufficient  time  has  elapsed  for  any  serious  amount  of 
condensation  to  occur  by  contact  with  cold  surfaces.  A  diagram 
from  a  2  horse-power  Otto-Langen  engine  from  Clerk's  work  on 
the  gas  engine  is  shown  in  Fig.  11-14.  This  diagram  shows 
that  the  expansion  during  the  working  stroke  continues  below 
that  of  the  atmosphere,  the  piston  evidently  being  taken  to  the 


248 


INTERNAL  COMBUSTION  ENGINES 


top  of  its  stroke  by  the  energy  stored  in  the   fly-wheel   at   the 
instant  of  explosion. 

The  igniting  device  used  consisted  of  a  constantly  burning 
flame  outside  the  working  cylinder  which  was  put  in  communica- 
tion by  a  slide  valve  with  the  ex- 
plosive charge  at  the  proper  time. 
The  large  sizes  of  this  engine  were 
governed  by  controlling  the  velocity 
of  discharge  of  the  exhaust  gases. 
The  more  the  exhaust  outlet  was 
throttled,  the  slower  the  descent  of 
the  piston,  and  hence  the  fewer  the 
number  of  cycles  in  unit  time. 

BRAYTON.  —  In  point  of  time 
the  next  important  invention  in 
the  art  of  producing  internal  com- 
bustion motors  was  made  by  an 
American,  George  B.  Brayton.  His 
engines  were  built  in  large  numbers 
and  possessed  many  advantages 
over  any  previously  made.  They  had  the  remarkable  distinc- 
tion of  being  the  only  motors  which  had  been  designed  in  which 
ignition  takes  place  at  constant  pressure,  the  form  of  the  dia- 
gram, already  shown  in  Chapter  I,  being  similar  in  many  respects 
to  that  of  the  steam  engine. 

Brayton  took  two  American  patents  for  his  engines;  first  the 
earlier  one  dated  April  2,  1872,  covered  an  engine  adapted  to 
burn  gas;  the  later  one,  patented  June,  1874,  covered  an  engine 
adapted  to  burn  liquid  hydrocarbon  or  petroleum.  Both  engines 
have  essentially  the  same  principle  of  operation,  the  air  and  com- 
bustible are  supplied  to  the  working  cylinder  under  pressure  for 
a  portion  of  the  stroke,  ignition  continues  during  the  admission 
of  the  air  and  combustible,  causing  an  increase  of  volume  without 
change  of  pressure.  The  supply  valve  closes  when  sufficient 
combustible  has  entered,  and  the  piston  finishes  its  stroke  by 
expansion.  Ignition  was  produced  by  a  constantly  burning 
flame  in  the  power  cylinder.  Wire  diaphragms  were  used  to  keep 
the  flames  from  striking  back. 

Of  the  two  forms  of  Brayton  engine,  the  gas  engine  never 


.3     .4      .5     .6      .7     .8 
STROKE 

FIG.  11-14.  —  Diagram, 
Otto-Langen  Engine. 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      249 

found  much  application  on  account  of  the  fact  that,  due  to  punc- 
turing the  diaphragm,  the  ignition  flame  would  sometimes  strike 
back  and  explode  the  compound  mixture  stored  in  the  reservoir. 


FIG.  11-15. —  Elevation,  Brayton  Oil  Engine. 

This  action  together  with  the  high  price  of  gas  led  to  the 
development  of  the  petroleum  engine.  Figs.  11-15  and  11-16 
show  the  construction  of  this  engine  very  clearly.*  The  engine 


FIG.  11-16.  —  Plan,  Brayton  Oil  Engine. 

consists  of  a  power  cylinder  a  and  an  air-compressor  cylinder  6, 
the  pistons  of  which  are  connected  to  the  walking  beam  c.  The 
air,  drawn  into  the  cylinder  b  through  an  automatic  valve,  is 

'•'•'  Giildner,  Entwerfcn  und  Borechnen  dor  Verbrennungsmotoren,  p.  91. 


250  INTERNAL  COMBUSTION  ENGINES 

discharged  through  the  valve  g  into  the  receiver  d  when  the 
pressure  has  reached  the  desired  point.  From  d  the  compressed 
air  flows  into  the  power  cylinder  when  the  valve  e  is  opened  by 
the  lever  shown,  through  the  action  of  a  cam  on  the  auxiliary 
shaft  h,  Fig.  11-16.  On  its  way  through  the  valve  the  air  is 
saturated  with  the  vapor  of  gasoline  or  petroleum  by  passing  a 
layer  of  saturated  felt  held  between  two  perforated  plates.  The 
small  pump  i,  shown  in  both  figures  and  actuated  from  the  cam 
shaft  h,  serves  to  keep  the  felt  saturated.  Just  below  this  car- 
bureting device,  a  needle  flame,  kept  supplied  with  gasoline  by 
the  pump  i,  is  kept  constantly  burning,  igniting  the  charge  as  it 
passes.  The  admission  valve  is  opened  as  the  working  piston 
reaches  its  upper  end  of  the  stroke.  The  mixture  therefore  burns 
as  the  piston  is  traveling  downward,  and  the  rate  of  combustion 
is  so  regulated  that  the  pressure  remains  practically  constant 
during  the  time  of  admission  Fig.  11-17  shows  'a  typical  work 

diagram.     The  card  from  the 
air  cylinder  is  of  course  just 
like     the     ordinary     air-com- 
pressor diagram. 
FIG.  11-17.  —  Power  Card,  Brayton  _,, 

En  ine  The  engine   was   governed 

by  cutting  off  the  mixture  at 

the  desired  point.  This  was  accomplished  by  making  the  admis- 
sion valve  cam  conical  and  sliding  it  along  the  shaft  h  by  means  of 
the  governor  shown,  thus  varying  the  time  of  opening  of  the  valve. 
This  oil  engine  was  a  thoroughly  practical  machine  and  found 
considerable  application.  Regarding  its  economy,  a  test  by 
Clerk  showed  the  following  figures: 

Diameter  of  Motor  Cylinder 8  " 

Stroke  of  Motor  Cylinder 12  " 

Diameter  of  Air  Cylinder 8  " 

Stroke  of  Air  Cylinder 6" 

Mean  R.  p.  m 201 

Mean  B.  KL  P 4.26 

Net  Indicated  H.  P 5.40 

Pump  H.  P 4.10 

Total  I.  H.  P 9.50 

Mechanical  Efficiency,  % 79.0 

Petroleum  pr  B.  H.  P.-hour,  gals    323 

The  fuel  consumption  shown  amounts  to  a  thermal  efficiency 
of  6  per  cent  on  the  brake. 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      251 

THE  OTTO  ENGINE.  —  The  Otto  engine  was  patented  by 
Nicholas  A.  Otto  of  Deutz,  Germany,  in  the  United  States, 
August  14,  1877,  and  in  England  about  one  year  earlier.  The 
engine  was  shown  with  great  success  at  the  Exposition  of  1878. 
It  was  called  the  "  Silent "  engine,  probably  in  contradistinction 
to  the  free  piston  engine  of  the  same  inventor. 

The  patent  taken  out  by  Otto  is  devoted  principally  to  a 
description  of  an  improved  method  of  introducing  air  and  gas 
into  the  cylinder  of  a  gas  engine,  in  layers  or  strata  so  as  to  make 
the  explosion  less  violent  in  its  nature.  The  patent  describes 
three  kinds  of  engines  to  which  his  process  could  be  applied,  viz., 
a  non-compression  engine,  an  engine  of  similar  structure  to  the 
non-compression  engine  but  in  which  the  charge  is  compressed 
by  external  means  before  passing  into  the  cylinder,  and  lastly 
the  now  common  four-cycle  engine  in  which  the  compression  is 
performed  in  the  working  cylinder  and  which  followed  in  its  mode 
of  operation  the  principles  laid  down  in  the  French  patent  of  Beau 
de  Rochas  in  1862. 

The  Otto  method  of  introducing  air  and  gas  in  separate  layers 
to  produce  slow  combustion  did  not  prove  to  be  of  practical 
value,  but  the  construction  described  in  Claim  3  of  the  American 
patent  not  only  revolutionized  all  previous  methods  of  gas  engine 
construction  but  formed  the  basis  for  all  subsequent  practice. 
This  claim  is  stated  as  follows: 

3.  A  gas-motor  engine  wherein,  by  one  out  stroke  of  the  piston,  separate 
charges  of  combustible  gaseous  mixture  and  air  are  drawn  into  the  cylinder, 
which  charges  are  compressed  by  the  in  stroke  and  then  ignited,  so  as  to  propel 
the  piston,  which  by  its  return  stroke  expels  the  products  of  combustion. 

The  Otto  engine  was  so  greatly  superior  to  all  the  earlier  ones 
in  economy  and  capacity  for  a  given  weight  and  regularity  of 
operation  that  it  soon  distanced  all  competitors.  Its  success  led 
to  numerous  infringements  in  Germany  and  England  and  in  each 
of  these  countries  a  patent  suit  was  brought ;  in  Germany  the  Otto 
patent  was  declared  invalid  because  of  the  earlier  patent  to  Beau 
de  Rochas,  but  in  England  it  was  sustained.  In  the  United 
States  no  patent  suit  was  brought,  although  there  were  doubtless 
many  infringements  before  the  patent  expired  in  1894. 

Figures  11-18  to  11-20  show  a  horizontal  cross-section,  a  side 


252 


INTERNAL  COMBUSTION  ENGINES 


view  and  an  end  view  of  an  Otto  engine  of  1884.*  In  this  engine 
the  admission  of  the  fuel  mixture  and  its  ignition  are  controlled 
by  the  slide  valve,  b.  This  valve  is  actuated  by  a  crank,  dy  and 
moves  forward  and  backward  across  the  cylinder  head.  The  gas 


FIG.  11-18.  —  Horizontal  Section  Otto  Engine  of  1884. 

valve,  g,  is  actuated  by  a  cam,  g',  upon  the  side  shaft,  /,  while  the 
exhaust  valve,  c,  of  the  now  usual  poppet  type,  is  actuated 
through  a  lever  by  means  of  a  cam,  e,  upon  the  same  shaft.  This 
shaft,  /,  turns  with  one  half  the  speed  of  the  crank  shaft.  The 


FIG.  11-19.  —  Elevation  of  Otto  Engine  of  1884. 

admission  slide  valve  is  held  against  its  seat  by  a  cover  plate. 
This  plate  contains  the  ignition  arrangements  and  air  and  gas 
ports,  which  latter  coincide  with  other  ports  through  the  valve 
proper  and  into  the  combustion  chamber,  a',  in  certain  positions 
of  the  valve.  The  gas  valve  is  connected  to  the  gas  port  in  the 
plate  by  a  bent  pipe,  d,  while  gas  is  furnished  to  the  ignition 
apparatus  by  the  small  forked  pipe  shown  in  Fig.  11-20. 

*  From  Guldner,  p.  43 


HISTOKY  OF  INTERNAL  COMBUSTION  ENGINE      253 


To  explain  the  operation  of  the  engine,  suppose  that  in  the 
position  shown  in  Fig.  11-18  the  piston  is  just  commencing  its 
suction  stroke.  The  exhaust  valve,  c,  has  just  closed  and  the 
port  in  the  valve  coincides  with  the  port,  i,  into  the  cylinder.  As 
the  piston  moves  outward,  only  air  is  drawn  in  for  the  first  part 
of  the  stroke,  because  the  cam  has  not  yet  opened  the  gas  valve,  g. 
A  little  later  g  opens  and  the  mixture  is  drawn  in  for  the  rest  of 
the  stroke.  At  the  outer  dead  center  the  valve  has  closed  the 
port,  i,  and  compression  next  takes  place.  By  the  time  the  pis- 
ton has  reached  the  inner 
dead  center,  the  valve  has 
moved  far  enough  over  to 
bring  the  ignition  cavity, 
k,  in  front  of  the  port,  i. 
The  flame  in  k  strikes  in, 
causing  the  charge  to  ex- 
plode. Expansion  and  ex- 
haust follow. 

The  above  method  of 
drawing  in  the  charge  was 
by  Otto  supposed  to  re- 
sult in  stratification,  i.e., 
according  to  his  views 
there  would  be  a  layer  of 

burned  gases  next  to  the      „ 

FIG.  11-20.  —  End  View  of  Otto  Engine 
piston,  then  a  layer  of  air  of  1884 

and  last  the  layer  of  mix- 
ture. He  also  claimed  that  this  arrangement  was  not  disturbed 
during  compression.  His  argument  was  that,  ignition  taking 
place  in  the  rich  mixture,  the  pressure  wave  would  soon  reach 
the  leaner  mixture  and  the  layers  of  air  and  burned  gas  in  suc- 
cession, and  "tone  down/'  so  to  speak,  in  its  intensity  so  as  to 
avoid  shock  to  the  engine  mechanism.  The  opinions  of  experts 
regarding  the  soundness  of  this  theory  are  divided  even  to-day. 
See  Chapter  IV. 

The  ignition  apparatus  used  in  the  earlier  Otto  machines,  up 
to  the  general  introduction  of  electric  ignition,  was  very  similar 
to  that  employed  by  Otto  in  the  free-piston  engine  some  ten  years 
earlier.  Fig.  11-21  shows  a  cross-section  through  the  ignition 


254 


INTERNAL  COMBUSTION  ENGINES 


cavities  in  plate  and  slide.  One  branch  of  the  forked  pipe,  shown 
in  Fig.  11-20,  supplies  a  constantly  burning  flame,  G,  Fig.  11-21, 
while  the  second  branch  fills  the  cavity,  B,  with  gas  which  gets 
its  air  supply  through  the  port,  C,  the  mixture  igniting  when  it 
strikes  the  flame,  G,  as  shown.  When  near  the  time  of  ignition, 
cavity  B  in  the  slide  is  cut  off  from  its  air  and  gas  supply,  but 
enough  burning  mixture  is  left  in  the  cavity  to  ignite  the  charge 
in  the  cylinder  when  B  registers  with  the  port  into  the  cylinder. 
Since  the  pressure  in  the  compression  chamber  is  so  much  higher 
than  that  in  the  cavity,  there  is  danger 
that  the  flame  will  be  blown  out  when 
communication  is  first  established.  To 
prevent  this,  just  before  the  cavity  and 
the  inlet  port  commence  to  register,  com- 
munication is  established  with  the  com- 
bustion chamber  through  a  very  fine 
opening,  thus  equalizing  the  pressures  in 
inlet  port  and  cavity. 

The  governing  arrangements  were 
simple  and  effective.  The  gas  valve 
cam,  #',  Fig.  11-19,  was  arranged  to 
slide  on  the  shaft,  /.  A  fly-ball  governor 
controlled  its  position,  and  when  the 
speed  rose  a  certain  amount  above  nor- 
mal, the  cam  was  pulled  far  enough  to  the 
left  to  cause  it  to  miss  the  valve  lever,  I. 


FIG.  11-21.— 

Ignition  Arrangements, 

Otto  Engine  of  1884. 


Thus  the  engine  received  no  gas   and  an  impulse  was  missed. 

Economy  tests  on  early  Otto  engines  were  made  by  Slaby  and 
Brauer,  1881,  Teichman  and  Boecking,  1887,  and  by  others. 
The  thermal  efficiencies  on  the  brake  ranged  from  9  to  12  per  cent. 
The  best  figure  obtained  by  Brauer  in  1886  on  a  Deutz  4  horse- 
power horizontal  engine  was  a  total  gas  consumption  of  29.9 
cu.  ft.  per  B.  H.  P.  hour,  which  corresponded  to  a  thermal  efficiency 
of  15.5  per  cent.  Tests  made  by  Brooks  and  Stewart  at  Stevens 
Institute,  Hoboken,  in  1882  on  a  6  B.  H.  P.  engine  show  about 
the  same  results. 

The  engine  shown  in  Figs.  11-18  to  11-20  is  from  the  design 
standpoint  a  well-built  machine,  and  shows  a  very  marked  ad- 
vance in  this  respect  over  all  earlier  forms.  It  will  be  noted  that 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      255 

the  cross-head  was  still  used.  This  was,  however,  soon  dispensed 
with,  substituting  a  trunk  piston,  and  thus  shortening  the  length 
of  the  machine.  Another  change  soon  instituted  was  the  substi- 
tution of  electric  for  flame  ignition. 

CLERK.  —  The  disadvantage,  inherent  in  all  four-cycle  ma- 
chines, of  receiving  a  power  impulse  only  once  in  four  strokes, 
led  other  inventors  to  experiment  with  the  two-cycle  engine 
which  gets. a  power  impulse  every  turn.  The  change  from  the  four- 
to  the  two-cycle  principle  seems  very  simple,  but  is  in  reality 


FIG.  11-22.  —  Vertical  Section,  Clerk  Engine. 

beset  with  many  difficulties.  Perhaps  the  earliest  fairly  success- 
ful worker  was  Clerk,  who  commenced  to  experiment  upon  two- 
cycle  engines  soon  after  Otto  perfected  his  four-cycle  machine. 
It  was,  however,  not  until  1880  that  he  succeeded  in  producing  a 
serviceable  machine.  Figs.  11-22  and  11-23,  both  from  Clerk, 
"The  Gas  and  Oil  Engine,"  show  a  vertical  and  horizontal  cross- 
section  respectively.  The  operation  of  the  engine  is  as  follows: 
In  Fig.  11-23  the  power  piston,  C,  has  just  reached  the  outer 
dead  center  and  the  main  bulk  of  the  exhaust  gases  have  escaped 
through  the  ports  E  E' .  In  the  meantime  the  displacer  piston, 
Z>,  which  on  its  previous  suction  stroke  has  drawn  a  mixture  of 
air  and  gas  into  B,  has  completed  about  half  of  its  in  stroke  and 


256 


INTERNAL  COMBUSTION  ENGINES 


displaced  the  mixture  into  G  and  A  through  the  connecting 
pipe,  W.  About  the  time  D  has  completed  its  in  stroke,  the  power 
piston,  C,  has  covered  the  exhaust  ports  on  its  return  stroke,  arid 
compression  ensues  in  the  main  cylinder.  The  cylinder  volumes 
are  so  proportioned  that  in  theory  no  mixture  can  be  lost  through 
the  exhaust  ports.  At  the  inner  dead  center  of  the  power  piston, 
C,  or  just  before,  the  igniting  cavity,  0,  Fig.  11-23,  comes  oppo- 
site the  port,  N,  and  the  charge  is  fired.  The  piston  is  impelled 
forward  and  the  next  charge,  drawn  into  B  in  the  meantime,  com- 
mences to  enter  the  space  G  as  soon  as  the  pressure  in  A  has 
fallen  enough,  after  the  beginning  of  exhaust,  to  cause  the  valve 
in  the  pipe  between  B  and  G  to  lift.  The  intermediate  valve 


FIG.  11-23.  —  Horizontal  Section,  Clerk  Engine. 

arrangement  is  shown  in  Fig.  11-22.  P  is  an  air  chamber.  The 
air  drawn  in  by  the  suction  of  the  displacer  piston,  7J,  passes 
through  the  valve,  H,  and  in  so  doing  is  mixed  with  gas  which 
enters  through  a  number  of  fine  holes  ih  the  seat  of  the  valve 
from  the  annular  space,  K.  On  the  in  stroke  of  the  displacer 
piston  the  mixture  under  some  pressure  comes  in  under  the  valve, 
F,  which  it  lifts  as  soon  as  the  pressure  of  the  exhaust  gases 
above  it  has  fallen  low  enough. 

The  difficulty  under  which  the  engine  labored  was  loss  of 
mixture  through  the  exhaust  ports  and  consequent  low  economy. 
Although  the  respective  volumes  of  the  two  cylinders  may  be  in 
the  proper  ratio,  the  charge  expands  by  heat  on  the  transfer,  and 
mechanical  agitation  favors  the  loss.  In  spite  of  this  defect 
shop  tests  on  2,  4,  6,  8,  and  12  horse-power  engines  in  1885  gave 
results  fully  equal  to  those  obtained  on  the  four-cycle  machine 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      257 


of  that  day.     The  following  table  shows  the  results  of  some  of 
these  tests. 


Horse-power 

2 

4 

6 

8 

12 

Dia.  Motor  Cyl.,  inches  .  .  . 
Stroke  Motor  Cyl.,  inches. 
Dia.,  Displacer,  inches.  .  .  . 
Stroke  Displacer.  inches  .  . 
R.  P.  M.  .  .  . 

5 
8 
6 
9 
212 

6 
10 
7 
11 
190 

7 
12 
7| 
12 
14fi 

8 
16 
10 
13 

14.9 

9 
20 
10 
20 

1  Q9 

I.  H.  P  
D.  H.  P  
Mech.  Eff.,%  
GasperB.H.  P.-hr.,  cu.  ft. 

3.62 
2.70 

74.7 
40.0 

8.68 
5.63 
65.0 
37.3 

9.05 
7.23 
80.0 
30.42 

17.38 
13.69 

78.8 
26.58 

27.46 
23.21 

84.5 
24.12 

Figures  11-24  and  11-25  show  a  power  diagram  and  a  pump 
diagram  from  a  6  horse-power  engine. 

4.  Period  of  Application.  —  It  is  intended  in  what  follows  to 
give  merely  a  brief  resume  of  the  further  development  of  the  in- 
ternal combustion  engine  say 
up  to  1897  and  to  reserve  a 
more  detailed  description  of 
the  most  important  forms  in 
the  market  to-day  for  the 
next  chapter. 

On   account    of    the   Otto     ''«•  1  ^  ~  Power  Card,  Clerk  Engine. 

patent,  which  practically  amounted  to  a  monopoly,  other  manu- 
facturers were  forced  to  turn  their  attention  to  the  development 

of  the  two-cycle  en- 
gine. How  Clerk  solved 
the  problem  with  fair 
success  has  been  already 
shown.  He  was  fol- 
lowed by  Wittig  and 
Hess  (1880),  Benz  (1884),  Sohnlein,  Giildner  (1893-1898),  Oechel- 
hauser  (1896)  and  Koerting  (1898)  in  Germany,  Robson,  Southal, 
and  Samson  in  England,  Benier  (1894)  in  France,  and  Mietz 
and  Weiss  in  the  United  States.  Many  of  these  engines  are 
in  the  market  to-day,  and  some  are  described  in  the  next 
chapter. 

With  the  fall  of  Otto's  claims  in  Germany  about  1885  the  field 


FIG.  11-25.  —  Pump  Card,  Clerk  Engine. 


258  INTERNAL  COMBUSTION  ENGINES 

became  free,  and  many  manufacturers  of  the  two-cycle  engine 
abandoned  it  for  the  more  simple  four-cycle.  The  fall  of  this 
patent  was,  in  a  sense,  a  misfortune  as  far  as  the  two-cycle  engine 
was  concerned,  as  it  held  back  the  development  of  that  type  of 
machine  at  least  ten  years.  It  is  only  within  the  last  six  or  eight 
years  that  the  very  obvious  advantages  of  the  two-cycle  principle 
again  received  the  attention  they  deserve.  On  the  other  hand, 
the  development  of  the  four-cycle  engine  after  1885  was  extremely 
rapid.  Thus  while  the  limit  of  power  was  about  4  B.  H.  P. 
in  1878  and  units  of  from  15-20  horse-power  could  be  had  in  1880, 
the  limit  soon  rose  to  100  horse-power  in  1889  and  200  in  1893. 
Blast  furnace  gas  called  for  units  of  600  horse-power  in  1898, 
while  to-day  engines  developing  up  to  4000  horse-power  are  being 
built.  With  the  increase  in  size  up  to  the  neighborhood  of  200 
horse-power,  there  comes  an  increase  in  thermal  efficiency.  Thus 
a  Crossley  engine  of  12  horse-power  soon  showed  a  gas  consump- 
tion of  24.3  cu.  ft.  of  illuminating  gas  per  B.  H.  P.  hour.  To-day 
efficiencies  exceeding  25  per  cent  on  the  brake,  with  lean  power 
gases,  are  not  rare,  and  Giildner,  by  intelligently  applying  sound 
principles  of  construction,  has  succeeded  in  obtaining  economic 
efficiencies  exceeding  30  per  cent. 

It  would  lead  too  far  for  the  scope  of  this  book  to  describe 
even  a  fair  percentage  of  the  various  four-cycle  engines  brought 
out  between  1885  and  1898.  The  most  prominent  names  con- 
nected with  the  development  of  these  engines  are  perhaps  Loutzki 
in  Germany  (1888),  Delamare-Debouteville  &  Malandin,  who  in 
1900  brought  out  the  first  large  blast  furnace  gas  engine,  in 
Belgium,  Charon  in  France,  Crossley  Brothers  in  England  (1892 
and  1898),  and  Westinghouse  in  the  United  States  (1896).  Four- 
cycle const  ant -pressure  oil  engines  were  developed  by  Capitaine 
(1889-91),  Brunnler  (1893-4),  and  Diesel  (1893-97)  in  Germany. 
The  Diesel  engine  is  to-day  one  of  our  most  important  internal 
combustion  engines,  and  is  considered  in  greater  detail  below. 
Among  the  delevopers  of  the  four-cycle  constant  volume  oil 
engine,  Daimler's  work  in  connection  with  the  high-speed  engine 
deserves  special  mention.  Other  engines  of  this  type  brought 
out  in  this  period  are  Spiel  (1884),  Capitaine  (1885-90),  Priest- 
man  (1889),  Hornsby-Akroyd  (1892),  Banki  (1894),  and  Hasel- 
wander  (1898). 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      259 

One  of  the  greatest  achievements  of  this  period  is  the  develop- 
ment of  the  Diesel  engine. 

DIESEL.  —  The  history  of  the  Diesel  engine  is  interesting. 
It  began  in  1893  when  Rudolf  Diesel,  in  a  pamphlet  entitled 
"Theory  and  Construction  of  a  Rational  Heat  Motor  to  replace 
the  Steam  Engine  and  other  existing  Heat  Engines/'  laid  down 
the  following  "  fundamental  requirements  for  a  perfect  com- 
bustion." 

1.  Attainment  of  the  highest  temperature  in  the  cycle,  not  by 
means  of  combustion  and  during  the  same,  but  before  and  inde- 
pendent of  it  by  compression  of  air  alone. 

2.  Gradual  injection  of  atomized  fuel  into  this  highly  com- 
pressed and  heated  air  so  that   during  combustion   no   rise  of 
temperature  takes  place,  i.e.,  the  combustion  shall  be  isothermal. 
For  this  purpose  the  process  of  combustion  cannot  after  ignition 
be  left  to  itself,  but  must  be  governed  from  the  outside  to  main- 
tain proper  relation  between  pressure,  volume,  and  temperature. 

3.  Correct  choice  of  weight  of  air  with  reference  to  the  heat- 
ing value  of  the  fuel  and  the  desired  compression  temperature, 
so  that  the  practical  operation  of  the  machine,  lubrication,  etc., 
shall  be  possible  without  water-cooling. 

It  is  interesting  to  follow  out  these  points  and  to. see  in  how 
far  their  object  has  been  attained. 

The  intended  fuel  was  coal  dust,  the  cycle  the  Carnot.  At 
the  very  outset,  however,  a  modification  was  made  in  the  cycle 
in  cutting  out  the  isothermal  compression  and  substituting  for 
it  one  stage  adiabatic  compression.  But  a  jacket  was  not  thought 
necessar-y,  and  in  fact  a  non-conducting  lining  for  the  cylinder 
was  demanded. 

As  a  consequence  of  the  above  pamphlet,  two  firms,  Krupp 
in  Essen  and  the  Maschinen-fabrik  Augsburg,  undertook  the  con- 
struction of  experimental  machines.  As  was  to  be  expected, 
further  changes  from  the  original  idea  were  necessary,  the  two 
most  important  of  which  were  the  substitution  of  oil  for  coal 
dust,  and  the  use  of  a  water  jacket. 

In  1898  the  experimental  stage  had  been  so  far  passed  that 
Schroter  could  report  test  figures  which  more  than  doubled  the 
thermal  efficiency  of  the  then  existing  Otto  engines.  The  final 
form  of  the  engine  as  now  constructed  is  shown  in  Figs.  11-26  to 


260 


INTERNAL  COMBUSTION  ENGINE^ 


11-28,   which   represents   a    Diesel    engine    built    by   Krupp   in 
1898.* 

The  internal-cylinder  construction  offers  nothing  new;  a  is 
the  suction  valve  for  air,  b  the  fuel  valve,  and  d  the  exhaust  valve. 
c  is  the  starting  valve  not  in  commission  during  ordinary  opera- 
tions. All  are  actuated  through  levers  by  cams  on  the  shaft,  /, 
which  is  operated  from  the  crank  shaft  through  the  intermediate 
shaft,  e',  h  is  the  air  pump  to  furnish  compressed  air  for  fuel 
injection  and  for  starting.  Both  of  these  are  taken  from  steel 


FIGS.  11-26  to  11-28.  —  Diesel  Engine,  1898. 

flasks  into  which  h  delivers;  i  is  the  oil  pump  under  control  of 
the  governor  which  regulates  the  amount  of  oil  per  stroke  to  the 
load. 

On  the  first  down  stroke,  the  engine  takes  air  through  a  and 
compresses  it  on  the  return  stroke  to  a  pressure  of  about  460 
pounds,  with  a  temperature  of  about  1100  degrees  Fahrenheit. 
Just  before  the  end  of  the  up  stroke  the  fuel  valve,  b,  is  opened 
to  a  width  of  only  a  few  hundredths  of  an  inch,  and  the  injection 
air,  previously  compressed  to  about  650  pounds  by  pump  h,  flows 

*  Guldner,  p.  101. 


HISTORY  OF  INTERNAL  COMBUSTION  ENGINE      261 

into  the  compression  chamber,  carrying  with  it  and  finely  atomizing 
the  oil  furnished  by  the  pump,  i.  The  oil  ignites  on  entering,  due 
to  the  high  compression  temperature.  In  spite  of  the  fact  that 
isothermal  combustion  is  intended,  the  lack  of  outside  control 
causes  a  rise  not  only  in  the  pressure  of  from  80-100  pounds, 
usually  not  very  noticeable  on  the  indicator  card,  but  also  a  rise 
of  temperature  approximating  1800  degrees  Fahrenheit.  Thus 
while  the  intended  mean  temperature  of  the  cycle  of  Diesel's 
pamphlet  was  about  350  degrees,  that  realized  in  actual  operation 
is  about  950  degrees  Fahrenheit.  The  time  during  which  the 
fuel  injection  valve,  b,  remains  open,  is  constant  -for  all  loads,  but 
the  effective  stroke  of  the  fuel  pump,  i,  ends  the  sooner  the  lower 
the  load,  thus  effecting  regulation. 

After  the  closing  of  b,  expansion  commences  and  is  followed 
by  exhaust  through  d  on  the  return  stroke. 

The  engine  is  started  by  the  compressed  air  furnished  by  h 
during  a  previous  operation  and  stored  in  a  tank.  To  start,  the 
cams  on  the  shaft,  /,  are  pulled  to  the  right  by  the  lever,  g.  This 
puts  the  valves  a,  b  and  d  out  of  commission  and  starting  valve 
c  in  commission.  On  placing  the  crank  just  beyond  the  upper 
center,  and  opening  the  tank  valve,  the  engine  takes  compressed 
air  for  a  few  turns  just  like  a  steam  engine  takes  steam.  When 
the  required  momentum  has  been  obtained,  the  cams  are  re- 
leased and  are  snapped  back  into  place  by  a  spring  at  the 
proper  time. 

The  history  of  the  development  of  the  Diesel  engine  is  interest- 
ing in  that  the  final  construction  departs  so  far  from  the  patented 
ideal  that  the  engine  of  to-day  does  not  seem  to  be  protected  by 
the  claims  of  that  patent.  The  fact  that  no  igniter  was  neces- 
sary was  only  incidentally  considered  by  Diesel,  and  is  not  ex- 
pressly covered  by  the  patent. 

The  first  test  figures  on  a  Diese!  engine  were  published  by 
Schroter  in  1897.  The  dimensions  of  the  engine  were:  Cylinder 
diameter,  9.85",  stroke  15.7",  rated  B.  H.  P.,  18-20.  The  fuel 
used  was  American  kerosene  having  a  heating  value  of  18400 
B.T.U.  The  following  table  shows  the  results  of  two  full  load 
trials  and  compares  them  with  some  of  the  theoretical  results 
figured  by  Diesel  in  his  pamphlet  of  1893.* 

*Guldner,  p.  107. 


262 


INTERNAL  COMBUSTION  ENGINES 


Diesel  Engine  of  1897 

Ideal  Engine  of  1893 

Load  '  

Full         Full 

R  p  M  

171.8        154.2 

300 

B  H  P  

19.87        17.82 

? 

Total  I  H  P 

27  85       24.77 

100 

Pump  HP  ...... 

1.29          1.17 

Net  I  H  P  .  . 

26.56        23.69 

100 

Oil  per  B.  H.  P.-hr.,  Ibs  
Cooling  water  pr  B  .  H  .  P.-hr.  ,  Ibs. 
Compression  Press.,  Atm  
Max.  Comb.  Pressure,  Atm  
Temp.  End  of  Compression,  °C  .  . 
Temp.  End  of  Combustion  
Indicated  Thermal  Eff  .,  %  
Mech  Eff  %  

.543          .523 
154           203 
32.5          32.5 
36             36 
550           550 
1600         1600 
33.7          34.7 
71.0               72 

.247  Ibs.  of  coal  per  I.  H.  P. 
Zero 
250 
250 
800 
800 
73 

Thermal  Eff.  on  Brake,  %  

25.2          26.2 

? 

It  is  clear  from  the  above  table  that,  although  the  engine  did 
not  realize  the  early  expectation  of  its  designer,  the  results  shown 

are  a  remarkable  step  in 
advance  as  regards  the 
economy  of  the  then  ex- 
isting internal  combustion 
engines.  To-day  even  bet- 
ter figures  are  frequently 
obtained.  E.  Meyer,  for 
instance,  has  lately  tested 

FIG.  11-29. -Regulation  Diagram,  Diesel      a    DieSel     enSine    showing 
Engine.  an  indicated  thermal  effi- 

ciency   exceeding    42    per 

cent.  Fig.  11-29*  shows  the  general  form  of  the  indicator  card 
obtained  from  Diesel  engine.  This  is  a  regulating  diagram,  the 
size  of  the  card  decreasing  with  the  load  by  shortening  the  cut-off. 

*  Giildner,  p.  109. 


CHAPTER   XII 

MODERN    TYPES    OF    INTERNAL    COMBUSTION    ENGINES 

THE  previous  chapter  brought  the  development  of  the  internal 
combustion  engine  up  to  1897.  Since  then  expansion  has  been 
very  rapid,  until  to-day  we  find  that  the  design  of  gas  engines 
has  been  standardized  in  the  most  important  particulars  just  as 
was  the  case  with  the  steam  engine  some  decades  ago.  It  is  in- 
tended in  the  present  chapter  to  give  a  brief  description  of  the 
most  important  engines  found  in  the  market  to-day.  An  ex- 
amination of  the  market  will  show  some  fairly  definite  divisions 
among  manufacturers  as  far  as  size  of  engine  made  is  concerned. 
Thus  there  are  but  a  half  dozen  firms  in  this  country,  and  a  few 
more  than  this  in  Europe,  who  make  engines  up  to  the  very  largest 
sizes.  It  is  comparatively  easy,  therefore,  to  describe  nearly 
all  of  these  various  engines,  and  this  is  very  desirable  on  account 
of  their  importance.  Next  we  find  a  somewhat  larger  number 
of  medium  sized  engines  of  various  types,  and  lastly  a  very  large 
number  of  engines  up  to  say  50  horse-power  serving  the  general 
commercial  field  for  small  powers.  It  is  of  course  impossible  to 
cover  the  last  two  classes  of  engines  to  any  great  extent.  The 
majority  of  these  engines'  do  not  differ  except  in  minor  details, 
and  for  these  reasons  the  following  list  has  been  confined  to  what 
seem  to  be  the  most  representative  machines  of  each  class. 

Regarding  the  general  features  of  design,  small  engines  are 
either  horizontal  or  vertical.  The  cylinders  are  almost  invariably 
single-acting,  multiplication  of  power  being  obtained  by  increas- 
ing the  number  of  cylinders.  The  vertical  offers  some  advan- 
tages over  the  horizontal  form,  in  that  the  foundation  need  not 
be  as  large  or  as  heavy.  Further  it  is  claimed  that  it  is  easier 
to  lubricate  the  cylinders  uniformly,  and  that  the  wear  on  the 
cylinder  is  less.  A  favorite  form  of  frame  for  this  type  of  engine 
in  this  country  is  the  box  frame  with  enclosed  crank  case,  using 
splash  lubrication.  Some  European  designers  object  to  this 

263 


264  INTERNAL  COMBUSTION  ENGINES 

form,  claiming  that  all  supervision  of  crank  pins  and  intermediate 
bearings  is  by  this  form  of  frame  rendered  impossible.  The  small 
two-cycle  machine  almost  invariably  uses  the  enclosed  crank  case 
for  the  pre-compression  of  the  mixture. 

What  has  been  said  of  the  small  machine  applies  in  general 
also  to  medium  sized  engines.  Vertical  machines  here  possess 
the  added  advantage  that  it  is  easier  to  dismount  them  by  means 
of  overhead  crane  than  is  tho  case  with  horizontal  machines. 
The  limit  to  a  vertical  engine  comes  in  the  head  room  required. 
For  this  reason  all  of  the  very  large  machines,  as  well  as  medium 
sized  double-acting  machines  which  require  a  cross-head,  are 
horizontal.  Another  reason  that  may  be  cited  is  that  it  is  easier 
to  operate  a  medium  sized  or  large  horizontal  engine  than  it  is  a 
vertical  because  all  climbing  or  mounting  platforms  is  avoided, 
and  the  whole  installation  is  more  completely  under  the  operator's 
eye.  Finally,  the  use  of  some  of  the  industrial  power  gases  favors 
the  use  of  the  horizontal  machine,  because  any  dust  carried  can 
be  much  more  easily  swept  out  of  a  horizontal  than  a  vertical 
cylinder  during  regular  operation. 

The  double-acting  engine  is  perhaps  not  used  as  widely  as  it 
deserves  to  be,  increase  in  power  being  generally  sought  by  multi- 
plying the  single-acting  cylinders.  There  is,  however,  to-day  no 
reason  why  double-acting  cylinders  are  not  as  reliable  as  the 
single-acting.  For  large  machines,  double-acting  cylinders  are 
almost  an  economic  necessity,  and  the  clumsy  four-cylinder 
double-opposed  large  engine  has  become  thoroughly  obsolete. 
The  largest  engines  of  to-day  are  double  or  twin  two-cylinder 
tandem  double-acting  engines. 

The  very  obvious  disadvantages  of  the  trunk  piston  can  be 
quite  successfully  overcome  for  small  and  medium  sized  machines, 
and  hence  it  is  almost  universally  employed  for  these  sizes.  But 
for  large  'machines  the  use  of  the  trunk  piston  is  indefensible, 
being  opposed  alike  by  considerations  of  manufacture  and  of 
reliable  operation.  The  fitting  of  large  pistons  of  this  type  offers 
grave  difficulties  in  the  shop,  and  in  operation  proper  lubrication 
is  difficult;  further,  the  main  office  of  the  piston  is  to  confine  the 
gases  without  leakage;  to  make  it  also  act  as  the  machine  member 
to  take  up  the  lateral  thrust  of  the  connecting  rod  may,  in  large 
machines,  seriously  interfere  with  its  main  purpose. 


MODERN   TYPES  OF  COMBUSTION  ENGINES        265 

The  crank  shaft  of  small  and  medium  sized  engines  is  nearly 
always  of  the  center-crank  type.  This  type  is  very  rigid  and, 
above  all,  transmits  the  stresses  equally  to  both  sides  of  the  frame. 
In  double  or  twin  machines,  however,  such  a  shaft  would  call  for 
four  main  bearings,  the  proper  alignment  of  which  might  cause 
some  trouble  in  large  engines  of  this  type.  For  this  reason,  some 
American  makers  prefer  the  side-crank  shaft,  which  is  a  much 
less  costly  shaft  to  make,  and  reduces  the  number  of  bearings  for 
a  twin  engine  to  two.  Of  course,  the  side-crank  frame  takes  up 
the  explosion  stresses  eccentrically,  and  therefore  has  to  be 
designed  heavier  than  the  center-crunk  frame.  On  account  of 
this  fact  and  the  generally  higher  stresses  in  gas  engine  frames 
as  compared  with  steam-engine  frames,  Fluropean  designers  will 
not  use  the  so-called  side  crank  or  Tangye  form  of  frame. 

The  period  of  experimentation  in  design,  and  of  freak  design, 
has  largely  passed  in  gas-engine  practice,  and,  as  mentioned  at 
the  outset  of  this  chapter,  standardization  has  made  welcome 
progress  during  the  last  few  years.  The  alcohol  engine,  now  in 
its  development  as  far  as  the  United  States  is  concerned,  does  not 
call  for  any  radical  changes  in  the  existing  designs  of 'liquid  fuel 
engines.  As  far  as  further  progress  is  concerned,  it  is  not  unlikely 
that  the  next  step  will  be  the  development  of  a  highly  efficient 
constant-pressure  gas  engine  after  the  manner  of  the  Diesel  liquid 
fuel  engines,  taking  up  the  thread  again  where  Brayton  left  it  in 
the  seventies. 

A.   Gas  Engines 

1.  SMALL  AND  MEDIUM  SIZED  ENGINP:S.  —  Among  the  best 
known  makers  of  small  and  medium  sized  gas  engines  in  this 
country  may  be  mentioned  the  Otto  Gas  Engine  Works  of  Phila- 
delphia, makers  of  the  Otto  engines;  the  Fairbanks-Morse  Com- 
pany; the  Jacobson  Machine  Manufacturing  Company,  of  Warren, 
Pa.;  the  Jacobson  Engine  Company,  of  Chester,  Pa.,  the  Struthers- 
Wells  Company  of  Warren,  Pa.,  makers  of  the  Warren  engine; 
the  Bruce-Meriam  Abbott  Company,  of  Cleveland;  the  Westing- 
house  Machine  Company;  the  Olds  Gas  Power  Company,  of 
Lansing,  Mich.;  the  De  LaVergne  Machine  Company  of  New  York, 
makers  of  the  four-cycle  Koerting  engines;  the  Weber  Gas  Engine 
Company  of  Kansas  City,  Mo.;  the  A,  H,  Alberger  Company  of 


266 


INTERNAL  COMBUSTION  ENGINES 


Buffalo,  makers  of  the  Buffalo  tandem  engines,  the  Foos  Gas 
Engine  Company  of  Springfield,  Ohio,  etc. 

In  most  cases  the  small  gas  engine  operates  on  illuminating 
gas,  natural  gas,  or  gasoline,  but  in  many  instances  attachments 
are  furnished  so  that  the  engine  can  be  run  on  either  gas  or  liquid 
fuel  as  desired.  Producer  gas  is  not  usually  employed  for  very 


FIG.  12-1.  —  Westinghouse  Engine. 

small  units.  A  10  to  15  horse-power  suction  gas  producer  for  hard 
coal  is  the  present  lower  limit  and  perhaps  the  exception,  while 
soft  coal  producers  in  their  present  state  of  development  do  not 
run  less  than  50  to  60  horse-power. 

The  Westinghouse  Gas  Engine.  —  The  cross-sectional  cut, 
Fig.  12-1,  shows  the  essential  parts  of  the  Westinghouse  vertical 
engine.  In  this  type  the  crank  mechanism  is  completely  enclosed, 
and  splash  lubrication  is  depended  upon  for  the  proper  oiling  of 


MODERN   TYPES  OF  COMBUSTION  ENGINES 


267 


the  intermediate  bearings,  the  crank  pins  and  the  pistons.  Both 
the  inlet  and  exhaust  valves  are  mechanically  operated  by  cams 
and  shafts  driven  from  the  main  shaft;  the  inlet  valve,  J,  by 
means  of  cam  B  and  lever  (7,  the  exhaust  valve  E  by  cam  A  and 
the  roller  lever  shown.  The  igniter,  operated  from  the  inlet  cam 
shaft,  is  located  at  F.  Gas  and  air,  after  passing  the  chamber  M 
in  the  proper  proportion,  enter  the  passage  N  on  their  way  to 
the  inlet  valves.  The  engine  is  governed  by  means  of  a  governor 
of  the  fly-ball  type  which  regulates  the  amount  of  mixture  enter- 
ing the  passage  N  (see  Chapter  XIV).  The  smaller  sizes  of  this 


FIG.  12-2.  —  Westinghouse  Engine. 

machine  have  two  cylinders,  and  can  generally  be  started  by 
hand;  the  larger  sizes,  above  about  85  horse-power,  have  three 
cylinders  and  are  generally  started  by  compressed  air,  which  is 
admitted  to  one  cylinder,  starting  the  engine,  while  the  other 
cylinders  operate  normally.  Figs.  12-2  and  12-3  show  general 
views  of  three-cylinder  machines. 

Engines  manufactured  under  the  Jacobson  Patents.  —  There 
are  two  firms  manufacturing  engines  under  these  patents,  the 
Jacobson  Engine  Company  of  Chester,  Pa.,  and  the  Jacobson 


268 


INTERNAL  COMBUSTION  ENGINES 


Machine  Manufacturing  Company  of  Warren,  Pa.  The  engines 
made  are  of  three  types,  hit-and-miss,  automatic  cut-off,  and 
throttling.  The  Warren  Company  make  hit-and-miss  engines 
from  2^  to  25  horse-power  and  automatic  engines  from  8  to  27 
horse-power.  The  Chester  Company  make  hit-and-miss  engines 
from  30  horse-power  up,  and  automatic  cut-off  and  throttling  en- 
gines from  33  horse-power  up.  All  of  these  engines  so  far  men- 
tioned are  single-acting.  The  automatic  cut-off  and  throttling 


FIG.  12-3.  —  Westinghquse  Engine. 

types  are  built  as  single-cylinder  or  as  tandem  or  twin-tandem 
units.  The  Chester  Company  now  also  undertake  the  building  of 
double  acting  automatic  cut-off  or  throttling  engine  as  tandem 
or  twin-tandem  units  up  to  any  power  desired. 

The  structural  features  of  the  engines  built  by  the  two  com- 
panies mentioned  are  of  course  very  nearly  the  same,  so  that  one 
description  will  do  for  both. 

The  general  features  of  the  hit-and-miss  machine  are  shown 
in  Fig.  12-4.  The  most  interesting  detail  of  the  design  is  perhaps 
the  removable  cylinder  bushing,  which  is  an  unusual  but  highly 
commendable  construction  for  small  engines.  This  not  only 
allows  of  choosing  the  proper  grade  of  metal  for  the  cylinder 
barrel,  but  thermal  stresses  are  also  avoided  by  admitting  of 


MODERN   TYPES  OF  COMBUSTION  ENGINES        269 

free  expansion,  in  this  case  against  the.  packing  at  the  head  of  the 
bushing.  On  account  of  the  manner  of  holding  it,  this  packing 
can  never  be  blown  out. 


FIG.  12-4.  —  Jacobson  Hit-and-Miss  Engine. 


FIG.  12-5.  —  Governing  Mechanism  of  Jacobson  Hit-and-Miss  Engine. 

The  inlet  valve  is  automatic,  and  is  held  in  a  separate  housing. 
The  manner  of  operating  the  exhaust  valve  and  the  governor 
control  are  shown  in  Fig.  12-5.  The  side  shaft  is  operated  by 
means  of  screw  gears,  which  is  the  most  satisfactory  way  of 


270 


INTERNAL  COMBUSTION  ENGINES 


transmitting  the  motion.  The  governor  is  of  the  fly-ball  type  and 
is  operated  by  the  lay  shaft.  When  the  speed  becomes  too  high, 
the  blade,  C,  Fig.  12-5,  put  in  position  by  the  governor,  engages 
the  block  A  on  the  exhaust  valve  lever,  prevents  this  lever  from 
returning,  thus  holding  the  exhaust  valve  open. 


"    VENT  TO  ATMOSPHERE 


FIG.  12-6.  —  Gas  Pressure  Regulator  for  Jacobson  Engines. 

Figure  12-4  also  shows  the  make-and-break  igniter.  One 
block  contains  both  electrodes  and  the  location  of  the  spark  is 
central  as  regards  the  volume  of  the  charge. 

This  engine  can-  be  run  on  either  gas  or  gasoline,  depending 
upon  whether  a  gas  regulator  or  a  carbureter  is  employed.  The 
type  of  regulator  used  is  illustrated  in  Fig.  12-6.  Its  construction 
is  very  simple,  there  is  nothing  apparently  to  get  out  of  order. 
It  is  claimed  that  this  regulator  furnishes  the  gas  to  the  engine 


MODERN   TYPES  OF  COMBUSTION  ENGINES        271 


FIG.    12-7.  —  Jacobson    Auto- 
matic Cut-off  Engine. 


under  atmospheric  pressure  at  all  times.  The  firm  makes  an 
attachment  which  allows  of  the  change  from  one  fuel  to  another 
at  a  moment's  notice. 

The  general  design  of  the  automatic  cut-off  is  the  same  as  for 
the  hit-and-miss  engine,  the  differ- 
ence being  in  the  governor  and  the 
valve  gear.  Fig.  12-7  shows  the 
method  of  operating  the  inlet  and 
exhaust  valves  and  the  igniter.  The 
valve  gear  is  shown  in  greater  de- 
tail in  Fig.  12-8.  The  seats  and 
stem  bushings  are  all  easily  accessi- 
ble and  replaceable.  The  exhaust 
valve  is  operated  in  the  ordinary 
way  by  a  cam  from  the  lay  shaft. 
For  the  inlet  valve  lever  an  eccen- 
tric is  used.  As  the  eccentric  rod 
R  rises,  it  "pushes  upward  the  valve 
lever  Q  at  the  right  end  and  opens 
the  inlet  valve.  The  inlet  valve  spindle  carries  two  discs,  the  main 
inlet  valve  and  the  gas  valve.  Just  before  the  exhaust  valve 
closes,  the  gear  commences  to  open  the  inlet  valve,  but  only  air 
enters  since  the  gas  valve  V  remains  closed.  The  air  thus  enter- 
ing serves  to  scavenge  out  the  combustion  chamber.  A  moment 
later  the  valve  spindle  has  descended  far  enough  for  the  set 
collar  on  the  spindle  to  depress  the  gas  valve;  after  which  the 
mixture  begins  to  enter  the  cylinder.  Both  valves  close  simul- 
taneously when  the  nose  of  the  eccentric  rod  R  is  forced  off  the 
end  of  the  valve  lever  by  the  action  of  the  inclined  plane  P.  The 
position  of  this  plane  is  determined  by  the  governor,  which  is  of 
the  fly-ball  type  and  directly  driven  from  the  main  shaft.  Thus 
the  valve  always  opens  at  the  same  point,  but  it  closes  sooner  or 
later,  depending  upon  the  load. 

Figure  12-9  shows  the  general  appearance  of  the  automatic 
cut-off  machine.  They  are  built  in  sizes  up  to  27  horse-power 
by  the  Warren  Company,  and  can  be  adapted  to  run  on  gasoline 
and  natural,  illuminating,  or  producer  gas.  The  twin  tandem 
type  is  shown  in  Fig.  12-10  and  is  built  in  sizes  above  100  B.  H.  P. 
for  producer  gas  and  above  120  B.  H.  P.  for  natural  gas  by  the 


272 


INTERNAL  COMBUSTION  ENGINES 


FIG.  12-8.  —  Valve  Gear,  Jacobsori  Automatic  Cut-off 
Engine. 

Chester  Company.     One-half  of  this  unit,  the  tandem  engine,  is 
built  in  sizes  from  60  B.  H.  P.  upward  for  natural  gas  and  from 

50  B.  H.  P.  upward  for  pro- 
ducer gas. 

The  Chester  Company's 
throttling  engine,  a  general 
view  of  which  is  shown  in 
Fig.  12-11,  differs  from  the 
automatic  cut-off  machine 
only  in  some  details  of 
valve  gear.  A  cross^-section 

FIG.  12-9. -Jacobin  Automatic  Cut-off     °f    this    enSine   is  shown  in 
Engine.  Fig.  12-12,  while  Fig.   12-13 


MODERN   TYPES  OF  COMBUSTION  ENGINES        273 


FIG.  12-10.  —  Jacobson  Twin-tandem  Automatic  Cut-off  Engine. 


FIG.  12-11.  —  Jacobson  Throttling  Engine. 


274 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES        275 


FIG.  12-13.  —  Valve  Gear,  Jacobson  Throttling  Engine. 

illustrates  the  valve  gear.  Both  valves  are  operated  by  cams. 
The  charge  passes  the  mixing  and  throttling  valve,  which  is  con- 
trolled by  the  governor  through 
the  reach  rod  shown. 

The  Bruce-Meriam-A bbott 
Engine.  —  The  Bruce-Meriam- 
Abbott  Company,  located  in 
Cleveland,  Ohio,  manufactures 
engines  for  natural,  illuminat- 
ing, and  producer  gas  and  for 
gasoline.  The  design  used  for 
natural  and  illuminating  gas 
and  for  gasoline  is  shown  in 
Fig.  12-14.  The  sizes  range 
from  12  to  250  horse-power, 
two-cylinder  up  to  125  horse- 
power, and  four-cylinder  above 
that  size.  The  design  of  cylin- 
der and  frame  is  along  conven- 
tional lines.  The  cam  shaft 

,u  ,  FIG.  12-14.  —  Bruce-Meriam-Abbott 

across  the  top  of  and  between  Engine 


276 


INTERNAL  COMBUSTION  ENGINES 


FIG.  12-15.  —  Detail   of  Bruce-Mer- 
iam-Abbott  Engine. 


the  cylinders  is  operated  through  spur  and  bevel  gears  as  shown. 
The  valves  are  of  the  poppet  type  and  are  located  in  the  head. 
Above  55  horse-power  they  are  held  in  separate  cages  which  are 
easily  removable.  The  cam  shaft  operates  these  valves  by  rocker 
arms  on  either  side.  This  construction  is  more  clearly  shown  in 

Fig.  12-15.  An  excellent  feature 
of  the  machine  is  the  purely  cy- 
lindrical form  of  the  combustion 
chamber. 

Governing  is  effected  by  a  gov- 
ernor of  the  fly-ball  type  operated 
by  the  lay  shaft.  The  governor 
sleeve  operates  one  end  of  a  lever 
passing  between  the  cylinders, 
the  other  end  supports  the  mix- 
ing valve,  the'details  of  which  are 
shown  in  Fig.  12-16.  Gas  and 
air  enter  the  annular  space  shown.  On  the  suction  stroke  of  the 
engine  the  gas  flows  into  the  space  surrounding  the  piston  valve 
and  mixes  with  the  air  by  flowing  out  through  the  port  about 
half  way  up.  The  two  combined  then  enter  the  interior  of  the 
valve  through  the  six  ports  shown;  from  this  chamber  the  mixture 
goes  to  the  engine.  The  position  of  the 
valve  controls  the- amount  of  throttling  and 
thus  regulates  the  weight  of  the  charge 
going  to  the  engine.  It  is  stated  that  from 
full  to  no  load  this  valve  has  to  move  only 
T^  inch. 

Jump  spark  ignition  is  used.  The 
method  of  supporting  the  spark  coil  and 
the  system  of  wiring  is  well  shown  in  Fig. 
12-15.  The  timer  is  very  simple.  There 
are  two  copper  pins  each  about  J-inch  di- 
ameter and  f  inch  long.  One  of  them 
projects  from  the  bottom  of  a  small  cup 
while  the  other  is  fastened  to  the  end  of  a  flat  spring,  and  dips 
down  in  the  same  cup.  The  spring  may  be  seen  at  A,  Fig.  12-15. 
The  cup  is  filled  with  oil  and  the  points  are  normally  held  apart 
a  small  distance.  Just  before  a  spark  is  desired  the  spring  is 


FIG.  12-16.  —  Mixing 
Valve,  Bruce-Mer- 
iam- Abbott  Engine. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        277 

depressed  by  means  of  a  cam,  the  circuit  is  made  by  bringing  the 
points  in  contact  and  the  spark  is  produced  at  the  moment  the 
cam  releases  the  spring.  What  amounts  to  an  outside  spark  gap 
(see  next  chapter)  is  provided  so  that  the  spark  may  be  watched. 

To  convert  any  gas  engine  of  this  design  into  a  gasoline  engine 
it  is  necessary  merely  to  furnish  a  fuel  pump  and  to  replace  the 
iron  piston  valve  of  the  mixer  by  brass  or  bronze  to  prevent  rust- 
ing. To  retain  the  high  compression  used  with  gas,  however, 
this  company  has  adopted  the  Banki  principle  of  injecting  water 
into  the  cylinder.  The  device  is  said  to  give  entire  satisfaction. 

For  producer  and  natural  gas  this  firm  makes  engines  ranging 
from  25  to  200  horse-power,  two-cylinder  units  up  to  90  horse- 
power, and  four-cylinder  above  that.  The  design  of  these  engines 
is  apparently  somewhat  different  from  those  above  described, 
Fig.  12-17,  the  principal  change  being  that  the  lay  shaft  evidently 
runs  alongside  the  cylinders  instead  of  between  them.  The  cylin- 
der and  frame  construction  is  otherwise  the  same,  but  the  interest- 
ing feature  about  the  design  is  the  fact  that  the  center  line  of  the 
cylinder  is  offset  about  one-half  the  length  of  the  crank  from  the 
center  line  of  the  main  bearing,  as  near  as  can  be  scaled  from 
the  drawing.  This  is  on  the  principle  of  the  Ramsey  crank 
mechanism,  the  idea  of  which  is  to  equalize  the  wear  due  to  the 
side  thrust  of  the  piston  against  the  cylinder  on  both  sides  of 
the  cylinder  and  to  improve  the  turning  moment.  Both  of  these 
aims  are  attained  with  a  moderate  offset  such  as  here  used. 

The  Fairbanks,  Morse  &  Company  Engines.  —  The  Fairbanks, 
Morse  &  Company  manufacture  a  number  of  different  types  of 
engines,  both  vertical  and  horizontal,  for  gas  and  liquid  fuel. 
The  general  features  of  the  horizontal  design  are  shown  in  Fig. 
12-18.  It  appears  from  this  that  the  exhaust  valve,  at  the  side 
of  the  cylinder,  is  mechanically  operated,  while  the  inlet  valve 
placed  in  the  head  is  automatic.  The  governor  is  placed  in  the 
fly-wheel  and  may  be  either  of  the  throttling  or  hit-and-miss  type. 
In  the  latter  case  it  operates  to  hold  the  exhaust  valve  open. 
The  ignition  gear  is  of  the  make-and-break  type,  arranged  so  that 
at  starting  the  spark  may  be  retarded. 

Engines  above  9  or  10  horse-power  are  fitted  with  a  self-start- 
ing device  which  consists  of  two  parts,  a  match  detonator  and  a 
hand  pump.  Both  are  shown  in  plan  in  Fig.  12-18  at  the  s;de 


278 


INTERNAL  COMBUSTION  ENGINES 


of  the  cylinder.  The  hand  pump  serves  to  pump  a  combustible 
mixture  into  the  cylinder,  with  the  crank  just  beyond  the  center, 
which  mixture  is  fired  by  igniting  a  parlor  match  inserted  into  the 
detonator.  The  pressure  so  generated  is  sufficient  to  start  the 
engine  under  some  load. 


FIG.  12-17.  —  Bruce-Meriam-Abbott  Engine  for  Producer  Gas. 

Engines  are  built  for  gasoline,  naphtha  and  distillate,  for 
kerosene,  for  alcohol,  and  for  gas.  In  each  case,  of  course,  the  fuel 
feeding  and  mixing  arrangements  differ  somewhat.  In  the  liquid 
fuel  engines  the  feeding  device  acts  positively,  a  pump  being  used 
to  ^  inject  the  proper  quantity  of  fuel  into  the  charge  of  air.  In 


MODERN   TYPES  OF  COMBUSTION  ENGINES        279 


the  gas  engine  there  is  instead  a  mechanically  operated  gas  valve. 
If  desired  the  engine  may  be  arranged  to  run  on  either  gas  or 


FIG.  12-18.  —  Fairbanks-Morse  Engine. 

liquid  fuel.     Fig.  12-19  illustrates  an  engine  having  these  features. 

The  same  company  also  builds  two  distinct  types  of  producer 
gas  engines.  The  first  of  these  has  the  general  features  of  the 
standard  horizontal  engine  above  described,  the  second  is  quite 
different,  as  shown  in  Fig.  12-20.  In  this  design  both  valves  are 
of  the  vertical  poppet  type,  mechanically  operated  from  the  side 
shaft,  the  inlet  valve  on  top, 
the  exhaust  at  the  bottom. 
As  in  the  other  Fairbanks  en- 
gines, the  ignition  is  by  make 
and  break.  The  governor  is 
of  the  fly-ball  type,  operated 
from  the  lay  shaft.  Regula- 
tion is  by  throttling  a  mixture 
of  constant  proportion. 

The  general  type  of  Fair- 
banks vertical  engine  is  shown 

in  Fig.  12-21.     These  engines     FlQ  12_19.-  Fairbanks_Morse  Engine 
are  built  for  any  kind  of  fuel.  for  Liquid  or  Gas  Fuel. 


280 


INTERNAL  COMBUSTION  ENGINES 


Governing  is  effected  by  throttling  the  mixture;  make-and-break 
ignition  is  used.     Although  the  crank  case  is  enclosed,  lubrication 

is  positive  instead  of  by  the 
splash  method  usually  em- 
ployed in  this  design. 

The  Koerting  Four-cycle 
Gas  Engine.  —  This  German 
machine  is  manufactured  in 
this  country  by  the  De  La- 
Vergne  Machine  Company  of 
New  York.  The  general  fea- 
tures of  the  design  are  clearly 
shown  in  elevation,  Fig. 
12-22,  and  the  two  cross-sec- 
tions, Figs.  12-23  and  12-24. 
FIG.  12-20.  —  Fairbanks-Morse  Producer  The  entire  design  gives  the 

impression  of  being  very  sub- 
stantial and  thorough.  The  frame  is  a  very  rigid  construction 
and  the  cylinder  is  supported  by  the  frame  throughout  the 
length.  The  cylinder  head 
is  a  somewhat  complicated 
casting.  The  inlet  and  out- 
let valves  are  placed  verti- 
cally over  each  other  and  are 
operated  by  cams  from  a 
lay  shaft.  The  combustion 
chamber  is  divided  by  a 
water-cooled  tongue  project- 
ing from  the  cylinder  head. 
The  purpose  of  this  projec- 
tion is  to  effectually  cool  the 
interior  of  the  combustion 
chamber  and  to  thus  draw 
down  the  compression  tem- 
perature, admitting  of  higher 
compression.  The  mixing  FIG.  12-21. —  Fairbanks-Morse  Vertical 
valve,  shown  at  the  left  of  Engine, 

the  "transverse  section  in  Fig.   12-24,  is  automatic.     Regulation 
is  effected  by  means  of  a  governor  of  the  Hartung  type  which 


MODERN   TYPES  OF  COMBUSTION  ENGINES        281 


it 

-S 


282 


INTERNAL  COMBUSTION  ENGINES 


operates  a  butterfly  throttle  valve  in  the  admission  passage,  as 
shown.  The  speed  is  thus  controlled  by  throttling.  In  engines 
exceeding  100  horse-power  the  pistons  are  water-cooled.  All 
engines  above  12  horse-power  have  electric  igniters  while  those 


below  this  power  use  the  hot  tube,  at  least  as  constructed  by  the 
parent  firm. 

The  Buffalo  Tandem  Engine.  —  This  engine  is  made  by  the 
A.  H.  Alberger  Company  of  Buffalo.     A  full  description  will  be 


MODERN  TYPES  OF  COMBUSTION  ENGINES        283 

found  in  an  article  in  Power  for  February,  1907,  from  which  the 
following  illustrations  are  taken.  Fig.  12-25  shows  a  general 
.view,  Fig.  12-26  a  vertical  cross-section,  and  Fig.  12-27  two 
cross-sections  of  the  valve  chest  at  right  angles  to  each  other. 


FIG.  12-24.  —  Valve  Gear,  Koerting  Four-cycle  Engine. 

The  engine  differs  materially  from  those  previously  described 
in  having  two  cylinders  in  tandem,  each  acting  on  the  four-cycle 
principle.  The  back  piston  is  made  like  an  ordinary  steam  engine 


284 


INTERNAL  COMBUSTION  ENGINES 


piston  since  there  is  no  side  thrust  in  this  cylinder.  Its  piston 
rod  passes  through  a  water-cooled  stuffing-box  as  shown.  The 
back  cylinder  head  is  a  simple  flat  plate  not  water-cooled;  all 


h. 


FIG.  12-25.  —  Buffalo  Tandem  Engine. 

parts  requiring  it,  however,  are  thoroughly  cooled.  The  valves 
are  of  the  double-guide  poppet  type  and  are  placed  side  by  side 
in  a  valve  chest  at  the  side  of  the  cylinder,  Fig.  12-27.  Cams 


FIG.  12-26.  —  Section  Through  Cylinders  and  Pistons  of  Buffalo  Gas  Engine- 

on  a  lay  shaft  operate  these  valves,  as  shown  in  the  transverse 
section,  Fig.  12-27.  The  make-and-break  igniter,  which  is  ad- 
justable during  operation,  is  placed  over  the  inlet  valve  at  the 


MODERN  TYPES  OF  COMBUSTION  ENGINES        285 

right  side  of  the  valve  chest.     The  exhaust  pipe  is  fastened  at 
the  left  side  as  shown  in  the  longitudinal  section  of  the  valve 


FIG.  12-27.  -*-  Valve  Details  of  Buffalo  Engine. 

chest.  The  jacket  water,  after  passing  through  the  jacket,  is 
made  to  enter  the  exhaust  pipe,  cooling  the  gases  and  thus  acting 
as  a  muffler.  The  mixing  and  governing  arrangements  of  this 


The  Valve  Cage 


FIG.  12-28.  —  Mixing  and  Governing  Arrangements  Buffalo  Engine. 

engine  are  shown  in  Fig.  12-28.     The  two  inlet  valve  chambers 
are  connected  by  a  header,  as  shown  in  Fig.  12-25.     At  the  center 


286  INTERNAL  COMBUSTION  ENGINES 

this  header  carries  the  mixing  valve.  This  valve,  Fig.  12-28,  is 
a  hollow  cylinder  divided  into  two  parts  by  a  transverse  partition. 
Each  half  has  a  number  of  slotted  ports  which  in  certain  positions 
of  the  valve  register  with  other  similar  ports  in  the  cage.  The 
valve  has  two  offices.  Its  position  up  or  down  in  the  valve  cage 
controls  the  ratio  of  air  to  gas.  If  moved  up  the  effective  gas  port 
area  is  reduced,  while  that  of  the  air  ports  is  increased  by  the  same 
amount,  and  vice  versa.  Thus  no  matter  what  the  gas  used,  the 
total  effective  area  is  in  all  cases  the  same.  Rotary  motion  of 
the  valve  controls  the  cut-off  of  the  mixture  along  the  suction 


FIG.  12-29.  —  Buckeye  Two-cycle  Engine. 

stroke.  This  action  is  controlled  by  a  Rites  inertia  governor 
which  operates  through  linkage  as  shown  in  Fig.  12-25. 

The  Buckeye  Two-cycle  Gas  Engine.  —  This  engine,  made  by 
the  Buckeye  Engine  Company  of  Salem,  Ohio,  illustrates  a  type 
of  medium  sized  two-cycle  engine.  The  following  description  is 
taken  from  Power,  September,  1906.  It  is  a  single-acting  scav- 
enging twin  engine  and  can  be  made  to  operate  also  on  gasoline 
or  distillate. 

The  present  engine  has  two  motor  cylinders,  with  cranks  set 
at  180  degrees,  two  fuel  pumps  and  two  air  pumps.  Fig.  12-29 
shows  the  side  of  the  engine  on  which  the  secondary  shaft  is 
located  and  gives  a  good  general  view  of  the  valve  gear.  Fig. 
12-30  is  a  sectional  elevation  of  one  element  of  the  twin  engine. 
The  piston  2  performs  a  double  duty;  in  addition  to  delivering 


MODERN   TYPES  OF  COMBUSTION  ENGINES        287 


the  power  of  the  explo- 
sions to  the  crank,  it 
compresses  the  charge 
•in  the  chamber  18  for 
delivery  to  the  com- 
bustion chamber.  The 
cross-head  6  is  in  the 
form  of  a  plunger  and 
acts  as  an  air  pump  and 
compressor  piston  in 
the  chamber  7.  The  ex- 
haust ports  are  opened 
by  the  piston  2,  as  usual 
in  engines  working  on 
the  two-stroke  cycle. 
These  ports  are  shown 
at  14,  14,  Fig.  12-30. 
Each  piston  compresses 
its  own  explosive  mix- 
ture, but  each  cross- 
head  plunger  delivers 
compressed  air  for  sca- 
venging to  the  combus- 
tion chamber  of  the 
other  half  of  the  engine 
unit.  The  cycle  of 
operation  is  as  follows: 
When  the  piston 
uncovers  the  exhaust 
ports,  the  scavenging 
valve  11  is  opened  by 
the  valve  gear  and  com- 
pressed air  at  about  8 
pounds  per  square  inch 
is  admitted  to  the  com- 
bustion chamber  from 
the  air  pump  of  the 
other  cylinder.  This 
air  blast  sweeps  out  the 


288  INTERNAL  COMBUSTION  ENGINES 

burnt  gases,  and  the  admission  valve  10  is  then  opened,  admit- 
ting a  charge  of  gas  and  air  from  the  compression  chamber  18; 
this  charge  is  also  at  a  pressure  of  about  8  pounds  per  square 
inch.  The  piston  further  compresses  the  charge  on  its  back- 
stroke, as  usual,  and  it  is  fired  by  an  electrical  igniter.  As  the 
piston  travels  back,  compressing  the  charge  in  the  cylinder,  it 
draws  a  fresh  charge  into  the  front  end,  3,  of  the  cylinder  and  the 
cross-head  plunger  of  the  other  half  of  the  unit  similarly  draws  in 
a  charge  of  air.  The  delivery  of  air  from  the  chamber  and  pass- 
ages 7,  20,  and  19  is  controlled  entirely  by  the  valve  11,  but  the 
intake  of  air  by  the  plunger  6  is  controlled  by  a  piston  valve  63,  Fig. 
12-31,  which  takes  air  from  the  chamber  68,  connecting  with  the 
atmosphere  through  the  base  of  the  engine,  and  delivers  it  to 
the  chamber  69,  which  is  connected  to  the  cross-head  cylinder  of 
the  other  half  of  the  engine.  The  piston  valve  62  takes  in  a  mix- 
ture of  gas  and  air  through  the  chamber  67,  which  is  connected 
with  the  supply  source,  and  delivers  it  to  the  fuel  pump  3,  Fig. 
12-30,  through  a  balanced  throttle  valve  60,  Fig.  12-31.  The  fuel 
pump  then  forces  the  mixture  back  through  the  throttle  valve  60 
to  the'  admission  valve  cage.  The  throttle  valve  thus  regulates 
both  the  quantity  of  mixture  drawn  in  by  the  pump  and  the 
quantity  delivered  by  the  pump  to  the  combustion  chamber. 
The  mixture  and  air-intake  valves  are  operated  by  connecting 
rods  from  a  rock-shaft,  as  indicated  in  Fig.  12-31;  the  rod  38 
actuates  the  corresponding  valves  for  the  other  half  of  the  engine. 
This  rock-shaft  is  oscillated  by  an  eccentric  on  the  main  shaft 
and  an  eccentric  rod. 

The  governor  is  of  the  fly-ball  spring-opposed  type  and  serves 
merely  to  control  the  position  of  the  balanced  throttle  valves  in 
the  fuel  passages.  Since  the  cylinder  is  filled  with  scavenging 
air  every  stroke,  the  variation  of  the  amount  of  mixture  admitted 
does  not  vary  the  compression  pressure  but  merely  varies  the 
richness  of  the  cylinder  contents. 

The  engine  is  equipped  with  both  make-and-break  and  jump- 
spark  igniters,  but  the  former  are  ordinarily  used. 

The  Fairbanks  Engine.  —  The  Fairbanks  improved  horizontal 
enigne  is  of  the  four-cycle  type  and  made  to  operate  on  gas  or 
on  gasoline,  distillate  or  alcohol. 

The  general  appearance  of  the  engine  is  well  shown  in  Fig. 


MODERN  TYPES  OP  COMBUSTION  ENGINES        289 


290 


INTERNAL  COMBUSTION  ENGINES 


12-32  which  shows  the  gas  engine 


FIG.  12-32.  —  Fairbanks  Engine. 

head  of  the  cylinder.  Each  valve 
and,  when  closed,  the  valve 
face  is  practically  flush  with 
the  wall  of  the  combustion 
chamber.  This  results  in  a 
combustion  chamber  of  very 
simple  form.  The  lay  shaft 
at  the  side  of  the  engine  is 
driven  by  two-to-one  gearing 
from  the  crank  shaft.  It  car- 
ries, Fig.  12-32,  first  the  bevel 
gear  for  operating  the  hit- 
and-miss  fly-ball  governor; 
second  a  clutch  arrangement 
for  making  and  breaking  the 
connection  between  the  inlet 
and  igniter  cam  sleeve  and  the 
lay  shaft;  third,  the  exhaust 
valve  cam,  and  lastly  the 
sleeve  carrying  the  inlet  valve 
and  igniter  cams.  The  gov- 
ernor acts  by  interposing  a 
pick  blade,  prevents  the  ex- 


from  the  governor  side,  while 
Fig.  12-33  gives  a  front 
view  of  the  same  ma- 
chine. The  cylinder  is 
partly  supported  by 
the  frame,  as  shown. 
Cylinder  jacket  wall 
and  cylinder  head  are 
cast  in  one  piece,  doing 
away  with  all  joints. 
Both  valves  of  the  pop- 
pet type  work  upward 
and  are  mechanically 
operated.  Fig.  12-34 
shows  the  position  of 
these  valves  at  the 

is  placed  in  a  separate  cage, 


FIG.  12-33.  —  Fairbanks  Engine. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        291 

haust  valve  lever  from  returning,  and  thus  blocks  the  exhaust 
valve  open.  In  this  position  a  projection  on  the  exhaust  valve 
lever  unlocks  the  clutch  above  mentioned,  breaks  the  connection 
between  lay  shaft  and  inlet  cam  sleeve,  causing  the  latter  to 
remain  stationary.  The  inlet  valve  then  fails  to  open  as  long  as 
the  governor  does  not  withdraw  the  blade.  It  is  possible  to 
change  the  speed  of  the  engine  through  a  certain  range  by  adjust- 
ing the  governor  during  operation. 

The  ignition  system  is  of  the  make-and- break  type,  as  is  clearly 
indicated  in  Fig.  12-33.  The  electrodes  are  contained  in  one 
block,  which  is  easily  removable  for  inspection. 


FIG.  12-34.  —  Cylinder  Construction,  Fairbanks  Engine. 

The  method  of  operating  the  gas  valve  by  means  of  the  main 
inlet  valve  lever  is  also  shown  in  Fig.  12-33. 

The  Fairbanks  gasoline  engine  is  in  all  respects  similar  to  the 
gas  engine  above  described,  except  that  the  mixing  valve  shown 
at  the  left  of  Fig.  12-33  is  replaced  by  a  simple  type  of  overflow 
carbureter  which  is  supplied  by  a  gasoline  pump  operated  by  a 
cam  on  the  lay  shaft. 

The  Philadelphia  Otto  Engine.  —  The  general  features  of  the 
design  of  this  engine  are  shown  in  Figs.  12-35  and  12-36.  These 
particular  drawings  refer  to  a  30  horse-power  illuminating  gas 
engine,  but  the  same  design  is  carried  out  in  all  horizontal  engines 
from  5  up  to  and  including  40  horse-power.  Excellent  features 
of  the  construction  are  the  separate  cylinder  liner  and  the  remov- 


292 


INTERNAL  COMBUSTION  ENGINES 


able  valve  cages  for  gas,  inlet,  and  exhaust  valves.  Make-and- 
break  electric  ignition  operated  by  a  crank  from  the  end  of  the 
lay  shaft  is  used. 


FIG.  12-35.  —  Philadelphia  Otto  Engine. 

The  producer  gas  engines  made  by  this  firm,  the  Otto  Gas 
Engine  Works  of  Philadelphia,  show  the  same  general  make-up. 
Fig.  12-37  gives  a  general  view  of  a  type  made  in  60,  75,  95,  and 
120  horse-power  sizes.  This  design  differs  from  that  of  Fig.  12-35 
mainly  in  that  the  cylinder  is  supported  also  near  the  end  by  an 
extension  of  the  frame. 


FIG.  12-36.  —  Philadelphia  Otto  Engine. 

The  suction  gas  engines  are  governed  by  controlling  the  fuel 
valve,  regulation  thus  being  effected  by  changing  the  quality  of 
the  mixture. 

The  Olds  Gas  Engine.  —  The  Olds  Gas  Power  Company  of 
Lansing,  Mich.,  build  two  types  of  gas  engines:  Type  G  from 


MODERN  TYPES  OF  COMBUSTION  ENGINES        293 

8  to  100  horse-power  and  Type  K  from  25  to  300  horse-power, 
both  being  horizontal  single-acting  four-cycle  engines. 


FIG.  12-37.  —  Philadelphia  Otto  Producer-gas  Engine. 

Type  G  is  illustrated  in  Fig.  12-38.  This  engine  may  be  used 
either  for  gas  or  gasoline.  There  appear  to  be  no  very  unusual 
features  in  its  general  design.  Both  inlet  and  outlet  valves  are 


FIG.  12-38.  —  Olds  Type  G  Engine. 

of  the  poppet  type,  but  an  auxiliary  exhaust  opening  is  used  to 
relieve  the  main  exhaust  valve.     The  exhaust  valve  is  mechani- 


294  INTERNAL  COMBUSTION  ENGINES 

cally  operated  by  means  of  a  straight  push  rod  and  cam.  Igni- 
tion is  by  make  and  break.  The  governor  is  of  the  hit-and-miss 
type  and  operates  to  hold  the  exhaust  valve  open.  The  mixing 
arrangements  are  not  specially  described  in  the  available  informa- 
tion on  this  engine. 

Type  K  engines  are  of  somewhat  different  design  and  embody 
in  their  make-up  the  best  and  most  advanced  ideas.  A  general 
view  of  the  machine  is  given  in  Fig.  12-39.  Among  the  excellent 
features  of  this  design  are  the  following:  The  jacket  wall  is  in- 
tegral with  the  frame.  The  cylinder  liner  is  made  of  a  grade  of 


FIG.  12-39.  —  Olds  Type  K  Engine. 

metal  especially  adapted  to  the  service  and  consists  of  a  straight 
cylinder  with  a  flange  at  the  outer  end.  This  flange  is  received 
into  the  frame  and  is  held  in  place  by  the  cylinder  head.  This 
construction  allows  of  even  and  unrestricted  expansion.  The 
cylinder  head  contains  the  openings  for  the  inlet  and  outlet  valve 
cages  and  is  designed  with  the  greatest  possible  regard  to  expan- 
sion and  cooling  stresses.  The  following  description  of  the  valve 
mechanism  is  taken  from  the  catalogue  published  by  the 
company. 

The  inlet  and  exhaust  valves  are  of  the  vertical  poppet  type, 


MODERN  TYPES  OF  COMBUSTION  ENGINES         295 

mechanically  operated  and  working  in  long  guides  in  the  same 
vertical  axis  with  the  inlet  valve  at  the  top  and  the  exhaust 
valve  at  the  bottom.  The  inlet  valve  and  gas  valve  have  a  com- 
mon stem  and  the  cage  is  so  arranged  that  a  thorough  mixing 
occurs  just  at  the  entrance  to  the  cylinder.  The  gas  valve  opens 
slightly  later  than  the  air  valve  and  by  special  construction  used 
a  perfect  seating  of  both  valves  is  assured  at  all  times.  On  the 
smaller  sizes,  by  removing  the  inlet  valve  cage  the  exhaust  valve 
is  perfectly  accessible,  while  on  the  larger  sizes  the  exhaust  valve 
may  be  removed  together  with  its  hollow  water-cooled  seat  with- 
out disturbing  the  inlet  valve.  .  This  is  easily  done  as  its  weight 
is  counterbalanced.  Both  valves  are  operated  by  a  single  cam 
which  is  designed  so  as  to  have  a  quick,  full  valve  opening,  with- 
out noise  or  clatter.  Valves  and  valve  ports  are  of  liberal  sizes 
so  undue  throttling  is  avoided.  The  valve  springs  are  of  the 
highest  grade  spring  steel,  and  rest  on  plates  which,  being  sup- 
ported on  ball  and  socket  joints,  do  away  with  side  thrust.  All 
parts  and  particularly  all  bearings  are  made  of  ample  dimensions 
with  provision  for  oiling  every  wearing  surface.  The  lay  shaft 
which  is  driven  from  the  crank  shaft  through  spiral  gears  operates 
the  valve  mechanism,  governor  and  ignition  mechanism. 

The  speed  is  controlled  by  a  governor,  apparently  of  the 
Hartung  type,  which  is  driven  from  the  lay  shaft  and  serves  to 
throttle  the  mixture  admitted  to  the  cylinder. 

Figure  12-40  gives  a  good  view  of  the  ignition  arrangements. 
The  current  is  supplied  by  a  low-tension  make-and-break  Bosch 
magneto,  the  operation  of  which  is  explained  in  Chapter  XIII. 
The  point  of  ignition  can  be  easily  changed  during  operation  by 
adjusting  the  lever  along  the  row  of  holes  A-R. 

The  Warren  Engines.  —  The  Struthers- Wells  Company  of 
Warren,  Pa.,  manufacture  various  types  of  engines,  both  hit- 
and-miss  and  throttling,  all  operating  on  the  four-cycle  prin- 
ciple. 

For  ordinary  power  purposes  the  firm  builds  the  single-cylinder 
hit-and-miss  engine  illustrated  in  Fig.  12-41.  This  engine  is  made 
in  sizes  from  10  to  90  horse-power.  Above  30  H.P.  the  instal- 
lations are  equipped  with  special  starting  devices. 

All  of  the  other  types  are  apparently  governed  by  throttling. 
The  next  higher  range  of  power,  35  to  200  horse-power,  is  covered 


296  INTERNAL  COMBUSTION  ENGINES 

by  the  two-cylinder  throttling  engine  shown  in  Fig.  12-42.     The 
manner  of  governing  is  clearly  indicated. 

A  special  type  of  the  two-cylinder  engine,  for  which  maximum 
economy  and  closest  regulation  is  claimed,  is  shown  in  elevation 
in  Fig.  12-43.  This  engine  is  made  in  two  sizes  only,  110  and 
125  horse-power.  From  the  vertical  section,  Fig.  12-44,  showing 
the  cylinder  construction,  it  is  seen  that  the  cylinder  barrel  and 
jacket  are  cast  in  one  piece.  The  valves  are  of  the  vertical  poppet 


FIG.  12-40.  —  Igniter  Details,  Olds  Type  K  Engine. 

type,  opening  upward,  and  are  placed  in  a  valve  cage  integral 
with  the  cylinder  head.  The  manner  of  operating  these  valves 
by  cams  and  levers  from  a  valve  shaft  running  across  the  engine 
under  the  cylinders  is  shown  in  both  Figs.  12-43  and  12-44. 
Governing  is  effected  by  throttling  the  mixture  in  the  supply  pipe 
just  before  it  divides.  The  centrifugal  governor  and  its  linkage 
are  indicated  in  Fig.  12-45.  In  some  cases  the  governor  is  located 
between  the  cylinders  as  shown  in  Fig.  12-43.  A  cross-section 
through  the  valve  chest,  Fig.  12-46,  shows  the  method  of  operat- 


MODERN  TYPES  OF  COMBUSTION  ENGINES        297 


FIG.  12-41. 


FIG.  12-42.  —  Warren  Throttling  Engine. 


298  INTERNAL  COMBUSTION  ENGINES 


FIG.  12-43.  —  Warren  Throttling  Engine. 


FIG.  12-44.  —  Vertical  Section  Warren  Throttling  Engine. 


Of  THE 

UNIVERSITY 

OF 


MODERN   TYPES  OF  COMBUSTION  ENGINES        299 


FIG.  12-45.  —  Plan  of  Warren  Two-cylinder  Engine 


FIG.  12-46.  —  Cross-section  through  Valve  Chest,  Warren  Two-cylinder  En- 
gine. 


300  INTERNAL  COMBUSTION  ENGINES 

ing  the  make-and-break  igniter,  and  the  location  of  the  starting 
valve  in  the  valve  chest  cover  just  above  the  exhaust  valve. 

Warren  engines,  covering  the  range  from  200  to  325  horse- 
power, are  of  the  tandem  single-acting  type,  a  general  view  of 
which  is  shown  in  Fig.  12-47.  The  cross-section,  Fig.  12-48,  shows 
the  cylinder  construction,  which  is  unique  in  some  of  its  features. 
The  back  part  of  the  main  frame  forms  the  jacket  wall  for  the 
front  cylinder.  The  cylinder  barrel  itself  is  cast  in  one  piece  with 
the  cylinder  head.  The  construction  of  the  back  cylinder  is 
similar.  The  distance  piece  between  the  two  cylinders  rests  on  a 
separate  base,  and  forms,  .for  a  portion  of  its  length,  the  jacket 
wall  for  the  rear  cylinder.  The  front  piston  is  of  the  ordinary 
trunk  type.  The  back  piston  is  longer  than  is  usual  in  pistons 
not  subject  to  side  thrust.  The  method  of  water-cooling  piston 
and  rod  is  clearly  shown. 

The  valves  are  of  the  vertical  poppet  type  held  in  separate 
cages  which  are  easily  removable.  The  exhaust  valves,  at  the  bot- 
tom of  the  cylinder,  are  water-cooled.  The  valve  gear  is  shown 
in  detail  in  Fig.  12-49.  Both  valves  are  operated  from  the  same 
cam  on  the  lay  shaft.  The  operation  of  the  exhaust  valve  is  clear. 
The  motion  of  the  inlet  valve  varies,  depending  upon  the  load. 
The  valve  opens  and  closes  always  at  the  same  time,  because  the 
lift  of  the  actuating  cam  is  not  changed  throughout  the  entire 
range  of  load.  The  governor,  however,  through  the  linkage  shown, 
controls  the  position  of  the  sliding  block  above  the  valve  lever, 
moving  it  in  or  out,  depending  upon  whether  the  load  falls  or  rises. 
This  block  acts  as  the  fulcrum  about  which  the  valve  lever  turns, 
and  hence  the  lift  of  the  valve  is  made  proportional  to  the  load. 
The  inlet  valve  stem  carries  the  gas  valve.  The  latter  opens 
somewhat  later  than  the  main  inlet  valve.  The  manner  of  mix- 
ing gas  and  air  is  clearly  indicated  in  the  figure.  Butterfly  valves 
in  the  air  and  gas  passages  serve  to  help  control  the  proportions 
of  the  mixture.  The  ignition  system,  operated  from  the  lay  shaft 
as  shown  in  Fig.  12-49,  is  of  the  make-and-break  type. 

The  Struthers- Wells  Company  also  builds  vertical  engines  up 
to  600  horse-power.  The  older  multi-cylinder  types  of  these 
machines  are  practically  nothing  but  two  or  three  separate  engines 
direct  connected.  Thus  a  450  horse-power  unit  now  in  operation 
consists  of  three  engines  with  two  fly-wheels  between  the  cylinders. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        301 


302 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES         303 


FIG.  12-49.  —  Valve  Gear  of  Warren  Single-acting  Tandem  Engine. 


304  INTERNAL  COMBUSTION  ENGINES 

In  the  later  designs  this  has  been  modified.  A  600  horse-power 
vertical  engine  lately  completed  is  of  the  four-cylinder  A-frame 
type  mounted  on  a  solid  bedplate  with  the  fly-wheels  at  the  ends. 

2.  LARGE  GAS  ENGINES.  —  Large  gas  engines  of  American 
design  are  manufactured  by  the  Westinghouse  Machine  Company, 
by  the  William  Tod  Company,  Youngstown,  Ohio,  by  the  Snow 
Steam  Pump  Company,  Buffalo,  by  the  Riverside  Engine  Com- 
pany, Oil  City,  Pa.,  and  by  the  Wisconsin  Engine  Co.,  of  Corliss, 
Wis.,  makers  of  the  Sargent  engine.  There  are,  however,  a  few 
other  firms  making  large  engines  of  foreign  design.  Thus  the 
De  La  Vergne  Machine  Company  of  New  York  make  the  Koerting 
two-cycle  engine,  and  the  Power  and  Mining  Machinery  Company 
the  Crossley  engine.  The  Allis-Chalmers  Company,  who  built 
the  Niirnberg  engine,  have  apparently  an  engine  on  the  market 
that  is  not  strictly  of  Niirnberg  design.  Besides  these  well- 
known  machines  made  in  this  country,  the  Premier  engine  made 
in  England,  the  Cockerill  engine  made  in  Belgium,  and  the  Ger- 
man Oechelhauser  and  Deutz  engines,  should  be  mentioned. 
The  Oechelhauser  and  Koerting  engines  are  made  under  license 
by  a  number  of  firms  in  Germany,  and  in  the  case  of  the  Koerting 
engine,  also  abroad.  While  it  has  in  general  been  easy  to  get 
sufficient  descriptive  material  on  the  above-mentioned  engines, 
this  does  not  apply  to  certain  machines  of  American  design,  and 
the  information  given  is  hence  somewhat  meager. 

The  Westinghouse  Horizontal  Engine.  —  There  seems  to-be 
available  practically  no  definite  information  on  the  constructive 
details  of  the  Westinghouse  horizontal  double-acting  tandem  en- 
gine.* The  older  type  apparently  used  the  center  crank  and  the 
combustion,  or  at  least  the  valve,  chambers  were  placed  at  the 
sides  of  the  cylinders.  The  later  types  of  horizontal  engines  built 
by  this  company  approach  much  nearer  to  established  European 
practice.  Thus  the  engines  installed  in  the  power  plant  of  the 
Warren  and  Jamestown  railway  system  have  the  valves  in  the 
central  lines  of  the  cylinders,  as  shown  in  Fig.  12-50.  The  latest 
design  is  shown  in  Fig.  12-51,  which  represents  a  3000  horse-power 
unit  for  the  power  plant  of  the  Carnegie  Steel  Company  at  Besse- 
mer, Pa.  In  this  type  the  side  crank  is  used,  but  outside  of  this 

*  A  full  description  of  the  Westinghouse  Engine  has  just  appeared  in 
Power,  April,  1908. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        305 


306 


INTERNAL  COMBUSTION  ENGINES 


nothing  is  definitely  known  to  the  writer  regarding  the  mechanical 
details.     An  interesting  development  of  very  recent  date  is  the 


FIG.  12-51.  —  Westinghouse  Double-acting  Tandem  Engine. 

Westinghouse  vertical  single-acting  tandem  engine  shown  in  Fig. 
12-52.  This  engine  was  built  by  the  British  Westinghouse  Elec- 
tric and  Manufacturing  Company.* 

The  Tod  Engine.  —  The  following  description  of  this  engine 
is  taken  from  the  Iron  Age  of  July  18,  1907: 

"The  general  ap- 
pearance of  the  engine 
is  shown  in  Figs.  12-53 
and  12-54.  The  cyl- 
inders are  arranged  in 
pairs,  two  cylinders 
being  connected  in 
tandem  to  each  crank 
pin.  The  valve  gear, 
igniter,  switchboard 
and  operator's  hand 
wheels  are  all  situated 
between  the  cylinders 
and  are  easily  accessi- 
ble from  an  operating 
platform  placed  just 

FIG.  12-52.  -  Westinghouse  Vertical  Single-        bel°W  the  level  °f  the 
acting  Tandem  Gas  Engine.  center  lines  of  the  cyl- 


*  W.  H.  Booth,  Cassier's  Magazine,  November,  1907. 


MODERN   TYPES  OF  COMBUSTION  ENGINES        307 


308 


INTERNAL  COMBUSTION  ENGINES 


MODERN   TYPES  OF  COMBUSTION  ENGINES         309 

inders  and  shaft.  The  foundation  level  under  the  cylinders  being 
several  feet  lower  than  under  the  frames,  leaves  ample  room  be- 
low the  cylinders  to  make  the  exhaust  valves,  etc.,  easily  acces- 
sible, a  very  desirable  but  somewhat  unusual  feature. 

"  The  cylinders  and  water  jackets  are  integral  and  cast  in 
halves,  secured  together  with  flanged  joints  at  the  center.  The 
cylinders  are  not  attached  directly  to  the  main  bedplates  nor  to 
each  other,  but  are  supported  by  the  tie  pieces  in  such  a  way 
that  the  barrels  themselves  are  entirely  free.  All  strains  are 
transmitted  through  four  heavy  forged  steel  tie  bolts  extending 
the  entire  length  of  the  cylinders,  and  attaching  directly  to  heavy 
lugs  on  the  bedplate.  This  obviates  the  transmission  of  the 
strains  through  the  cylinder  walls,  and  contributes  to  accessibility 
and  the  easy  removing  of  parts.  The  pistons  are  of  steel,  with 
cast-iron  junk  rings,  and  the  pistons  and  rods  are  water-jacketed 
in  the  usual  manner.  Adjustable  tail-rod  supports  take  the  weight 
of  the  pistons  and  rods  from  the  cylinders. 

"  The  valve  gear  is  driven  by  eccentrics,  eliminating  entirely 
the  cam  drive,  which  has  been  an  objectionable  feature  of  many 
of  the  gas  engines  heretofore  built.  There  is  one  eccentric  for 
each  end  of  each  cylinder,  which  drives  both  the  inlet  and  exhaust 
valves  —  an  arrangement  that  reduces  the  number  of  parts. 
The  eccentrics  are  mounted  on  two  lay  shafts  running  parallel 
to  the  axes  of  the  cylinders.  The  latter  are  driven  by  a  cross 
shaft,  which,  in  turn,  derives  its  motion  from  two  eccentrics 
mounted  on  the  main  shaft.  The  inlet  valves  are  on  top  of  the 
cylinders,  and  the  exhaust  valves  on  the  bottom.  The  inlet  valve 
proper  is  of  the  mushroom  type,  sealing  the  ports  from  the  pres- 
sure in  the  cylinders.  The  main  valve  is  operated  by  a  rolling 
lever  and  returned  to  its  seat  by  a  spring.  The  mixing  valves 
and  governor  valves  are  of  radial  gridiron  type,  and  are  located 
in  the  upper  section  of  the  valve  bonnet.  The  mixing  valves 
may  be  operated  individually  or  collectively  by  a  suitable  hand 
mechanism.  The  governor  valve  which  controls  the  admission 
of  gas  has  constant  travel,  the  time  of  opening  being  controlled 
by  the  governor  by  either  increasing  or  decreasing  the  angle  of 
advance  of  the  crank  which  operates  them,  since  the  engine  is  of 
the  constant-compression  type. 

"The  governor  is  of  the  fly-ball  pattern  and  is  in  duplicate, 


310  INTERNAL  COMBUSTION  ENGINES 

one  controlling  the  operating  valves  on  each  side  of  the  engine. 
The  two  are  driven  by  Morse  chains  through  a  flexible  coupling, 
and  are  connected  by  a  cross  rod  which  may  be  removed  in  case 
it  is  desired  to  operate  either  side  of  the  engine  alone. 

"Each  end  of  each  cylinder  is  equipped  with  two  igniters,  one 
operated  mechanically  and  the  other  by  a  solenoid.  Either  may 
be  used  independently  or  the  two  together.  The  igniters  are 
under  control  of  the  governor,  and  when  the  engine  is  at  rest  are 
automatically  thrown  back  to  the  dead  center.  The  ignition  is 
on  the  make-and-break  system,  using  direct  current  at  90  volts, 
supplied  by  a  motor  generator  set,  which  is  so  designed  that 
either  end  may  be  used  as  a  motor  or  a  generator,  or  both  may  be 
used  as  generators  by  driving  directly  from  the  engine  shaft. 
Connected  in  series  with  each  igniter  is  a  tell-tale  lamp  on  the 
switchboard,  giving  a  positive  indication  as  to  whether  or  not  the 
igniters  are  sparking,  short-circuited  or  burnt  out." 

The  Sargent  Engine.  —  The  Sargent  complete  expansion 
engine,  made  by  the  Wisconsin  Engine  Company  of  Corliss,  Wis., 
is  shown  in  general  elevation  in  Fig.  12-55  and  in  transverse  sec- 
tion in  Fig.  12-56.  As  far  as  the  constructive  details  of  this  en- 
gine are  concerned,  it  has  the  merit  of  great  simplicity.  The 
engine  is  built  as  a  double-acting  tandem.  There  is  but  one  valve 
to  control  admission  and  exhaust  for  each  end  of  each  cylinder, 
and  but  a  single  cam  to  perform  these  various  offices,  while  a 
second  cam  operates  the  igniter.  The  lay  shaft  is  driven  from 
the  main  shaft  by  a  pair  of  worm  gears.  The  governor  is  of  the 
inertia  type,  the  Rites,  and  operates  to  advance  or  retard  the 
lay-shaft,  thus  controlling  the  time  of  cutting  off  the  admission 
of  the  incoming  charge  to  the  cylinder.  This  construction  is 
decidedly  different  from  that  used  by  other  designers. 

The  combination  valve  is  shown  in  cross-section  in  Fig.  12-56. 
Its  operation  is  described  as  follows : 

"Gas  is  piped  to  the  chamber  A  in  the  sub-base  and  air  to  the 
chamber  B,  which  pass  through  the  cylinder  supports  to  the 
chambers  A'  and  B',  ready  to  pass  into  the  mixing  chamber 
when  the  cam  depression  M  N  passes  the  roller  and  the  ports  F 
in  the  piston  valve  register  with  the  ports  E  and  D  in  the  bush- 
ing. When  the  piston  valve  goes  down  to  this  position,  the  con- 
fined air  in  the  piston  valve  dash-pot  forces  open  the  poppet  valve, 


MODERN  TYPES  OF  COMBUSTION  ENGINES         311 


I 


312 


INTERNAL  COMBUSTION  ENGINES 


thus  giving  free  admission  to  the  charge.  When  the  point  N 
of  the  cam  reaches  the  roller,  it  is  forced  down,  while  the  other 
end  of  the  lever  goes  up,  carrying  the  piston  valve  which  cuts  off 
the  admission.  The  poppet  valve  seats  and  both  valves  remain 


FIG.  12-56.  —  Transverse  Cross-section  Sargent  Engine. 

in  normal  position  during  compression,  ignition,  and  expansion, 
or  until  the  point  L  on  the  cam  pushes  the  roller  down  and  the 
piston  up,  which  opens  the  poppet  and  the  exhaust  gases  pass 
out  through  the  ports  K  and  the  elbow  W  to  the  exhaust  pipe 
under  the  floor. 

"The  poppet  valve  seals  the  opening  in  the  combustion  chamber 
during  the  compression  and  inflammation,  and  the  piston  valve, 


MODERN  TYPES  OF  COMBUSTION  ENGINES        313 

holding  against  no  pressure,  works  loosely  in  its  bushing,  cutting 
off  the  admission  and  guiding  the  exhaust. 

"  As  the  poppet  valve  controls  both  the  inlet  and  outlet  gases, 
both  the  valve  and  seat  keep  cool  and  need  to  be  ground  not  over 
once  or  twice  a  year.  The  mechanism  is  simple  and,  as  the  roller 
is  always  bearing  on  the  cam,  the  valve  motion  is  practically 
noiseless." 

By  revolving  the  piston  valve  by  the  index  wheel,  the  blind 
port  S  varies  the  mixture  to  suit  the  gas  whether  it  has  100  or 
1000  B.  T.  U.  per  cubic  foot. 

The  fundamental  idea  of  the  Sargent  engine  is  to  get  complete 
expansion  of  the  charge  in  the  cylinder.  In  the  ordinary  engine, 
which  at  full  load  draws  in  the  charge  to  the  full  stroke  of  the 
piston,  or  nearly  so,  the  terminal  pressure  is  anywhere  from  25 
to  50  pounds,  and  the  final  temperature  over  1000  degrees  Fah- 
renheit. Sargent  claims  that  his  engine,  cutting  off  the  stroke  at 
full  load  at  three-quarters  of  the  suction  stroke,  will  show  a  ter- 
minal pressure  slightly  above  atmosphere  and  a  temperature  of 
about  400  degrees  Fahrenheit.  The  system  of  speed  regulation 
by  cutting  off  at  various  points  along  the  suction  stroke  is  one 
used  by  several  makers,  but  in  nearly  all  cases  the  engines  cut  off 
at  nearly  full  stroke  for  full  load,  that  is,  at  full  load  the  ratio  of 
compression  is  nearly  equal  to  the  ratio  of  expansion.  In  the 
Sargent  engine  the  ratio  of  expansion  always  exceeds  the  ratio 
of  compression,  and  a  lowering  of  the  terminal  pressure  and 
temperature  is  of  course  the  result.  There  is  no  doubt  that  this 
lowering  of  the  temperature  has  a  great  deal  to  do  with  any 
success  that  the  use  of  a  combination  valve  such  as  described 
above  may  have.  In  the  Sargent  engine  the  rated  power  is 
developed  when  the  governor  cuts  the  admission  off  at  three- 
quarter  stroke;  the  rest  of  the  stroke  may  be  considered  potential 
over-capacity.  In  spite  of  the  fact  that  ordinary  experience 
shows  a  gas  engine  to  be  most  efficient  when  it  is  developing  its 
maximum,  not  the  rated,  load  as  long  as  normal  speed  is  main- 
tained, the  claim  is  made  for  this  engine  that  its  best  efficiency 
is  obtained  when  cutting  off  at  three-quarter  stroke. 

The  Koerting  Two-Cycle  Engine.  —  The  Koerting  engine  is  of 
German  design,  made  in  this  country  by  the  De  La  Vergne  Machine 
Company  of  New  York.  This  is  one  of  the  two  successful  large 


314  INTERNAL  COMBUSTION  ENGINES 

two-cycle  gas  engines  .in  Europe,  the  other  being  the  Oechel- 
hauser,  not  made  in  America.  Koerting  two-cycle  engines  are 
now  made  by  several  German  firms,  whose  constructions  differ 
somewhat  among  themselves  and  from  the  parent  design,  mainly 
in  frame  and  governor  details.  The  latter  seem  to  have  ah  im- 
portant bearing  upon  the  amount  of  work  done  by  the  pumps. 
The  type  made  by  the  De  La  Vergne  Machine  Company  is  best 
illustrated  from  the  catalogue  of  the  firm.  Fig.  12-57  shows  a 
cross-sectional  elevation  and  a  plan  of  this  machine,  used  in  this 
case  as  a  blowing  engine.  It  is  seen  that  the  engine  has  but  a 
single  cylinder  which  is  double-acting.  There  are  thus  exactly  the 
same  number  of  power  impulses  per  turn  as  in  a  single-cylinder 
steam  engine.  The  piston  is  very  long,  about  seven-eighths  of  the 
stroke,  and  is  of  course  water-cooled.  This  makes  it  necessary 
to  support  its  weight  at  the  cross-head  and  at  a  tail-bearing  to 
save  both  cylinder  and  stuffing-boxes.  At  the  side  of  the  power 
cylinder  there  are  a  gas  and  an  air  pump  which  furnish  gas  and 
air  by  separate  passages  to  the  mixture  inlet  valves  at  the  top  of 
the  cylinder.  The  manner  of  driving  "these  pumps  from  a  side 
crank  and  of  operating  the  piston  valves,  which  control  them, 
by  means  of  rocker  arms  driven  by  an  eccentric  from  the  main 
shaft,  is  clearly  shown  in  Fig.  12-58.  Fig.  12-59  illustrates  the 
valve  shaft  side  of  a  partially  constructed  machine  and  shows  the 
manner  of  operating  the  inlet  valves  and  igniter  gear.  The 
exhaust  gases  are  taken  care  of  by  a  ring  of  ports  in  the  middle 
of  the  cylinder.  These  ports  are  uncovered  by  the  piston  alter- 
nately on  each  side  (see  Fig.  12-57). 

The  operation  of  the  engine  is  as  follows: 

It  will  be  seen,  from  Fig.  12-58  that  the  pump  crank  is  in  the 
neighborhood  of  100  degrees  ahead  of  the  main  crank,  i.e.,  when 
the  latter  is  at  either  dead  center  the  pumps  have  completed 
about  one-half  their  stroke.  From  the  beginning  of  its  discharge 
stroke  the  air  pump  B,  Fig.  12-60,  has  forced  its  charge  of  air  into 
the  passage  leading  to  the  main  inlet  valve  and  has  forced  some 
of  this  air  also  partly  up  to  the  gas  passage,  which  is  the  inner 
concentric  passage  surrounding  the  inlet  valve  stem.  In  the 
meantime  the  piston  of  the  gas  pump  A,  the  motion  of  which  has 
been  exactly  the  same  as  that  of  the  air  pump  piston,  has  been 
allowed  to  shove  back  part  of  its  charge  into  the  gas  suction  pipe. 


MODERN   TYPES  OF  COMBUSTION  ENGINES         315 


316 


INTERNAL  COMBUSTION  ENGINES 


r 


« 

'So 
W 


MODERN  TYPES  OF  COMBUSTION  ENGINES        317 

At  the  moment,  therefore,  when  the  exhaust  gases  have  nearly 
completely  escaped  from  the  main  cylinder  through  the  ring  of 
ports,  and  the  main  inlet  valve  is  opened,  there  is  at  first  a  rush 
of  air  from  both  the  air  and  gas  passages.  This  serves  to  drive 
the  remainder  of  the  exhaust  gases  out  of  the  cylinder.  A  mo- 
ment later  the  gas  pump  starts  to  deliver  gas  and  the  mixture 
enters  the  cylinder.  By  the  time  the  power  piston  has  covered 
the  exhaust  ports  on  its  return  stroke,  the  air  and  gas  pistons 


FIG.  12-59.  —  Valve  Gear  of  Koerting  Two-cycle  Engine. 

have  reached  the  end  of  their  stroke,  the  inlet  valve  closes  and  the 
mixture  is  compressed  in  the  power  cylinder.  Ignition  is  by 
electric  spark. 

The  speed  of  Koerting  two-cycle  engines  is  controlled  by  pro- 
portioning the  amount  of  gas  to  the  load.  In  the  American  type 
this  is  accomplished  by  putting  butterfly  throttle  valves  /-/,  Fig. 
12-60,  in  the  discharge  passages  of  the  gas  pump.  The  position 
of  these  valves  is  controlled  by  the  governor,  which,  as  some  of 
the  other  illustrations  show,  is  of  the  centrifugal  type.  This 
method  of  pump  control-  is  open  to  the  objection  that  if  the 


318 


INTERNAL  COMBUSTION  ENGINES 


gas  used  is  at  all  dirty,  the  frictional  resistances  soon  become  so 
great  as  to  render  the  governor  inoperative.  Some  of  the  im- 
provements of  the  later  Koerting  engines  have  been  devoted  to 
this  very  point.  A  modified  design  of  gas  pump  is  that  of  Klein 
Bros.,  Dahlbruch,  Fig.  12-61.*  In  this  construction  the  piston 
forces  the  charge  back  into  the  suction  space  through  the  ports 
shown  at  the  middle  of  the  cylinder,  for  one-half  the  stroke.  The 
amount  of  gas  delivered  to  the  discharge  passage  during  the  last 


FIG.  12-60. 

half  depends  upon  the  position  of  the  small  overflow  piston  valves 
near  the  bottom.  This  is  controlled  by  the  governor  through  the 
linkage  shown.  Another  point  that  has  given  some  trouble  in 
the  first  designs  of  Koerting  engines  is  the  fact  that  the  time 
available  for  the  opening  and  closing  of  the  inlet  valve  was  but  a 
very  small  part  of  the  time  of  one  revolution.  The  inertia  actions 
were  very  severe  and  hence  the  engine  speed  was  somewhat  re- 
stricted. This  difficulty  has  been  overcome  in  an  elegant  way  in 
the  design  of  the  Siegener  Maschinensban  A-G  as  shown  in  Fig. 
12-62.  Here  the  lay  shaft  moves  only  at  ane-half  the  speed  of 

*  Hoffman,  Zeitschrift  d.  V.  d.  I.,  September  15,  1906. 


MODERN  TYPES  OF  COMBUSTION  ENGINES         319 


FIG.  12-61.  —  Gas  Pump,  Koerting  Two-cycle  Engine,  Klein  Bros. 


FIG.  12-62.  —  Modification  of  Inlet  Valve  Gear, 
Koerting  Two-cycle  Engine. 


320  INTERNAL  COMBUSTION  ENGINES 

the  main  shaft,  the  same  as  in  four-cycle  engines,  but  the  valve  is 
opened  twice  for  every  turn  of  the  shaft. 

Reinhardt  states  that  the  Koerting  engine  is  well  adapted  to 
blowing  service  because  it  starts  easily  under  load  and  is  certain 
in  its  operation  through  a  wide  range  of  speeds. 

The  Riverside  Engine.  —  This  engine  is  made  by  the  Riverside 
Engine  Company  of  Oil  City,  Pa.,  and  embodies  in  its  details 
several  features  decidedly  different  from  those  of  other  large 
engines.  Fig.  12-63  shows  the  heavy  duty  double-acting  tandem 
type  and  illustrates  the  peculiarity  of  the  valve  construction  very 
clearly.  Besides  this  type,  this  firm  also  builds  single-acting, 


FIG.  12-63.  — Riverside  Heavy  Duty  Double-acting  Tandem  Gas  Engine. 

single-cylinder  and  twin  engines,  and  single-acting  tandem  engines. 
One  of  the  single-acting,  single-cylinder  engines  is  illustrated  in 
Fig.  12-64.  The  following  is  a  description  of  the  main  features 
of  the  double-acting  machine.  It  applies  with  little  modification 
also  to  the  single-acting  type.  Fig.  12-65  shows  in  cross-section 
the  cylinder,  valve  and  piston  details  of  the  double-acting  engine 
and  will  serve  as  an  aid  in  following  the  description  of  these  parts. 
The  main  frame  or  bed  is  of  the  heavy  duty  tangye  rolling-mill 
type  with  bored  guides  and  main  bearings  cast  in  a  single  piece, 
and  is  of  great  weight  and  extreme  rigidity.  The  cylinder  end 
of  main  frame  is  squared  similar  to  cross-section  of  cylinder,  and 
has  machined  holes  for  receiving  the  tie  bars  which  attach  the 
cylinder.  The  design  of  this  frame,  with  its  bored  guideway,  is 
such  that  a  large  portion  of  the  metal  is  above  the  center  line, 
making  it  exceptionally  stiff. 


MODERN   TYPES  OF  COMBUSTION  ENGINES         321 

The  shaft  is  of  side  crank,  built-up  type  and  is  machined  all 
over. 

The  cylinders  are  made  in  two  halves,  with  heads  and  valve 
chest  cast  integral  without  joints  or  packing,  and  are  held  rigidly 
to  the  main  frame  by  four  heavy  steel  tie  bars  which  take  all 
tension  strains.  The  cylinders  are  mounted  on  a  heavy  cast-iron 
sole  plate,  having  a  machined  top  surface  which  keeps  cylinders 
in  alignment,  permits  perfect  freedom  for  expansion  ami  contrac- 
tion, and  by  removing  distance  piece,  cylinders  can  be  slid  end- 
wise on  sole  plate,  giving  easy  access  to  interior  of  cylinder,  pistons 


Fi<;.  12  ()4.  —  Riverside  Single-art ing .Single  Cylinder  (las 
Engine. 

and  piston  rings.  Rings  can  be  cleaned  or  changed  without  dis- 
turbing piston  or  rod.  The  sole  plate  makes  a  drip  pan  under  all 
the  cylinders,  keeping  oil  drip  from  foundation.  The  exhaust  and 
inlet  piping  is  attached  to  the  sole  plate,  hence  no  piping  except 
the  water-jacket  piping  has  to  be  disturbed  when  cylinders  are 
moved.  There  is  no  overhead  piping  or  wiring  to  interfere  with 
traveling  crane. 

Both  inlet  and  exhaust  valves  are  of  the  semi-balanced  water- 
cooled  poppet  type,  operated  in  a  vertical  position.  All  water 
passing  to  the  cylinder  jacket  passes  through  valves  first,  giving 
perfect  and  positive  cooling  without  any  attention  whatever. 

The  balancing  pistons  run  in  renewable  liners  and  are  lubri- 
cated positively.  These  pistons  form  a  large  and  perfect  guide, 


322 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES        323 

assuring  positive  alignment  for  these  valves  indefinitely.  The 
valve  seats  are  renewable  and  are  located  slightly  below  bottom 
of  cylinder  bore,  so  that  all  foreign  substances  are  swept  from  the 
cylinder  at  each  exhaust  stroke.  All  valves  are  readily  removed 
from  the  top  of  the  cylinder  without  disturbing  cam  shaft. 

Piston  and  piston  rods  are  water-cooled,  the  water  entering 
through  a  telescopic  joint  connected  to  side  of  cross-head.  Cir- 
culation through  each  piston  is  positive  and  the  overflow  is  so 
arranged  that  pistons  are  kept  full  of  water.  Water  passages 
through  piston  and  rod  are  large  and  easy  so  that  not  over  ten 
pounds'  pressure  is  required  for  circulation.  The  overflow  is 
visible  so  that  water  cannot  come  to  a  boiling-point  without 
attracting  engineer's  attention.  A  heavy  tail-rod  support  and 
adjustable  shoe  is  provided  for  carrying  weight  of  pistons  and 
rod.  The  construction  of  the  piston  rod  is  such  that  a  piston  in 
either  cylinder  can  be  removed  without  disturbing  the  other 
cylinder  or  the  connecting  rod,  cross- head  or  any  part  of  the  valve 
gear. 

The  valve  gear  of  the  Riverside  engine  is  very  simple  and  con- 
sists of  a  single  shaft  mounted  on  top  of  the  engine,  running  in 
self-oiling  bearings.  This  shaft  runs  at  one-half  the  speed  of  the 
main  shaft  and  carries  the  inlet  and  exhaust  cams,  cams  for 
operating  the  oil  pumps,  and  the  timers  for  ignition  system: 
Power  is  transmitted  to  the  inlet  and  exhaust  valves  by  an  inlet 
and  exhaust  lever  hung  on  a  single  pin.  All  cams  are  keyed 
rigidly  to  the  cam  shaft.  This  construction  makes  a  minimum 
number  of  joints  subject  to  wear.  Ample  adjustments  are  pro- 
vided for  taking  up  wear. 

Ignition  is  by  an  improved  method  throughout,  consisting  of 
two  magnetically  operated  spark  plugs  in  each  cylinder.  The 
sparking  points  being  in  series  with  the  magnet  coils  give  a  posi- 
tive external  indication  by  the  movement  of  the  armature  as  to 
whether  the  spark  takes  place  within  the  cylinder.  The  timing 
is  electrical;  no  gearing  or  mechanical  trips  being  used,  simply 
a  No.  14  stranded  wire  running  through  iron  armored  conduits 
leads  to  each  plug. 

The  timer  is  mounted  on  the  secondary  shaft  and  is  built  in  a 
heavy,  substantial  manner.  The  contacts  are  of  the  wipe  type 
and  are  made  of  tool  steel;  and  are  adjustable  for  wear.  A  visible 


324  INTERNAL  COMBUSTION  ENGINES 

indicating  spindle  shows  the  amount  of  contact.  The  entire 
wearing  parts  of  timer  are  run  in  oil,  which  prevents  burning  of 
the  contacts  and  reduces  wear  to  minimum.  Wiring  from  the 
timer  to  each  spark  plug  is  protected  by  a  five  ampere  enclosed 
fuse;  thus,  should  any  spark  plug  become  damaged  or  short-cir- 
cuited, it  would  have  no  effect  on  the  rest  of  plugs.  Any  spark 
plug  can  be  removed  and  replaced  while  the  engine  is  in  opera- 
tion. 

The  time  of  ignition  in  all  cylinders  can  be  adjusted  simul- 
taneously, and  by  an  individual  adjustment  the  time  of  ignition 
in  any  cylinder  can  be  adjusted  independently.  All  of  these 
adjustments  can  be  made  when  the  engine  is  in  operation. 

The  method  of  starting  the  double-acting  engine  is  as  follows: 

A  gas-engine  driven  air  compressor  is  provided  for  supplying 
compressed  air  for  starting  this  engine,  air  to  be  stored  in  a  suitable 
steel  receiver.  The  pneumatic  starting  gear  on  the  engine  consists 
of  two  shifter  pistons  mounted  within  the  valve  lever  carry- 
ing pin.  These  pistons  are  shifted  by  throwing  a  small  three- 
way  cock  which  applies  compressed  air  to  one  side  of  the  piston, 
which  in  turn  moves  the  valve  levers  f  inch,  bringing  the  cam 
rollers  in  line  with  an  auxiliary  cam  which  puts  all  the  valves  in 
both  ends  of  one  cylinder  into  two-cycle  action,  or,  in  other  words, 
makes  a  poppet  valve  air  or  steam  engine  out  of  this  cylinder, 
which  permits  the  engine  being  started  on  any  stroke  and  on 
either  quarter.  The  operation  being  entirely  automatic,  the 
engine  will  run  as  long  as  compressed  air  is  applied.  The  other 
double-acting  cylinder  continues  to  operate  as  a  four-cycle  gas 
engine  and  takes  up  its  explosions  after  the  first  revolution. 
Compressed  air  is  then  shut  off  from  the  starting  cylinder  and  the 
three-way  cock  reversed,  which  permits  the  cam '  levers  being 
returned  to  their  normal  position  and  that  cylinder  immediately 
goes  into  four-cycle  action  and  takes  up  its  explosions  on  the  next 
revolution.  The  starting  gear  adds  practically  no  complication 
to  the  engine  as  the  regular  inlet  and  exhaust  valves  are  used  for 
distributing  the  air.  There  are  no  extra  shaft  or  auxiliary  valves 
and  no  tappings  into  the  cylinders.  There  is  only  one  compressed 
air  pipe  leading  to  the  sole  plate,  air  being  delivered  into  the  fuel 
duct  and  entering  the  cylinders  via  the  inlet  valves. 

The  Crossley  Engine.  —  This  English  engine  is  made  in  this 


MODERN   TYPES  OF  COMBUSTION  ENGINES        325 

country  by  the  Power  and  Mining  Machinery  Company  of  New 
York,  and  known  as  the  American  Crossley. 

These  engines  are  built  as  single-cylinder,  two  cylinder-opposed 
and  double-opposed  units,  sizes  ranging  from  50  to  1300  B.  H.  P. 
This  design  differs  radically  from  that  of  other  large  engines  in 
that  the  single-acting  cylinder  is  retained  up  to  the  largest  sizes, 
i.e.,  the  design  is  in  a  way  nothing  but  an  enlargement  of  the  small 
four-cycle  machine.  It  is  fundamently  the  same  design  employed 
at  first  by  the  Deutz  Company  for  their  large  engines,  but  has 
been  given  up  by  them  some  years  ago  in  favor  of  double-acting 
engines. 

Figures  12-66  and  12-67  show  a  general  elevation  and  a  cross- 
sectional  elevation  respectively  of  the  single-opposed  type.  The 
cylinder  castings  are  securely  bolted  to  each  end  of  a  central  frame 
casting.  Both  connecting  rods  work  on  one  crank  pin.  The 
pistons  are  water-cooled.  The  cylinder  proper  is  a  separate  liner, 
resting  at  the  crank  end  in  the  jacket  casting  and  held  at  the  head 
end  by  the  cylinder  head.  The  head  carries  the  gas  and  inlet 
valves,  while  the  exhaust  valve  is  placed  in  a  separate  casting. 
The  position  of  inlet  and  exhaust  valve  is  shown  in  Fig.  12-68. 
Both  are  operated  in  a  horizontal  position  by  means  of  bell  cranks 
by  cams  on  a  lay  shaft.  In  this  respect  the  engine  differs  from 
most  others  in  which  the  valves  are  nearly  always  vertical.  The 
objection  to  the  horizontal  form  is  at  least  partly  overcome  by 
giving  the  exhaust  valve  a  guide  at  each  end.  This  valve  is 
water-cooled,  as  is  necessary  in  large  machines.  The  lay  shaft  s, 
Fig.  12-66,  is  operated  by  spiral  gears,  and  actuates  the  main 
inlet,  the  cut-off  valve,  the  gas  valve,  the  exhaust  valve,  and  the 
igniter  gear. 

Gas  and  air  enter  the  mixing  chamber  M,  Figs.  12-66  and 
12-69  through  a  proportioning  valve,  the  air  direct  and  the  gas 
through  a  special  gas  valve.  From  here  the  mixture  passes  a 
multi-port  cut-off  valve,  which  surrounds  the  valve  stem  of  the 
inlet  valve  and  is  shown  in  greater  detail  in  Fig.  12-70.  This  cut- 
off valve  is  operated  from  the  lay  shaft  through  the  rocker  arm 
C,  Fig.  12-71.  The  governor,  shown  in  plan  in  Fig.  12-69,  serves 
to  shift  the  fulcrum  /  of  the  rocker  arm  c,  Fig.  12-71,  thus  cutting 
off  the  mixture  supply  to  the  main  inlet  valve  earlier  or  later  as 
the  load  demands.  Should  the  load  drop  so  far  that  the  com- 


326 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES         327 


328 


INTERNAL  COMBUSTION  ENGINES 


FIG.  12-68.  —  American  Crossley  Engine,  Inlet  Valve 
at  A,  Exhaust  Valve  at  E. 


r-S 


FIG.  12-69.  —  Details  of  Valve  Gear,  American  Crossley  Engine. 


MODERN   TYPES  OF  COMBUSTION  ENGINES        329 


bustion  becomes  sluggish  under  very  low  loads,  the  engine  auto- 
matically shifts  over  to  the  hit-and-miss  governing  by  the  gover- 
nor withdrawing  the  block  b,  Fig.  12-69,  thus  keeping  the  gas 
valve  closed  altogether. 
In  multi-cylinder  engines 
the  point  at  which  this 
occurs  is  so  adjusted 


is    so 

that  one  cylinder  after 
another  changes  over  to 
the  latter  system  of  regu- 


FIG.  12-70.  —  Inlet  Valve,  American  Crossley 
Engine. 


lation  and  not  all  of  them  at  the  same  time. 

The  American  company  for  some  time  adhered  to  hot  tube 
ignition,  but  some  of  the  later  engines  were  fitted  with  make-and- 
break  electric  ignition. 

The  Snow  Engine.  —  The  Snow  Steam  Pump  Company  build 


FIG.  12-71.  —  End  View,  American  Crossley  Engine. 

two  types  of  horizontal  double-acting  four-cycle  machines,  called 
respectively  Type  "A"  and  Type  "B."  Both  of  these  designs 
differ  radically  from  the  construction  of  other  large  gas  engines 


330 


INTERNAL  COMBUSTION  ENGINES 


in  that  the  valves  are  placed  in  chambers  at  the  side  of  the  cylin- 
ders. There  are  reasons  for  and  against  this  construction,  the 
main  disadvantage  being  perhaps  the  cut-up  form  of  the  com- 
bustion chamber.  Some  of  the  many  advantages  are  outlined 
below. 

Type  B  engines  are  built  in  single-cylinder  units  from  20  to 
125  horse-power,  and  in  tandem  units  from  80  to  500  horse- 
power. The  general  features  of  the  design  are  shown  in  eleva- 
ion  in  Fig.  12-72  and  in  cross-section  in  Fig.  12-73. 


FIG.  12-72.  —  Snow  Type  B  Gas  Engine. 

The  most  notable  installations  of  Type  A  engines  is  found  in 
the  Martin  station  of  the  San  Mateo  Power  Company  in  Cali- 
fornia. This  station  at  present  contains  three  of  the  twin- 
tandem  units,  a  fourth  is  in  course  of  erection,  and  the  foundation 
is  laid  for  a  fifth.  Fig.  12-74  shows  a  general  view  of  the  station, 
and  also  serves  to  give  a  general  idea  of  the  appearance  of  the 
engines.  The  engines  of  the  Martin  station  were  described  in 
great  detail  by  C.  P.  Poole  in  an  article  in  Power,  January  14  and 


MODERN   TYPES  OF  COMBUSTION  ENGINES         331 


21,  1908,  to  which  the  writer  is  indebted  for  the  following  infor- 
mation: 

Figure  12-75  shows  in  cross-section  the  main  features  of  the 
design,  while  Fig.  12-76  is  a  transverse  cross-section  through  one 
of  the  valve  chambers  to  show  the  valve  construction.  Each  cylin- 
der of  the  twin  tandem  unit  is  42  inches  in  diameter  by  60-inch 
stroke.  The  engines  are  direct  connected  to  Crocker- Wheeler 
generators  rated  at  4000  K.W.  each.  They  are  capable,  however, 
of  carrying  momentarily  an  overload  of  33  per  cent,  and  have 
demonstrated  their  ability  to  carry  15  per  cent  overload  con- 
tinuously. These  figures  make  these  units  the  largest  gas  power 


/HJl2X         L,  ^fir=rraaiS 


FIG.  12-73.  —  Cross-section  of  Snow  Type  B  Gas  Engine. 

engines  in  the  world.     The  fuel  used  is  an  oil-water  gas  made  by 
the  Lowe  process. 

The  main  frame  is  of  the  side  crank  type.  The  cylinders  are 
cast  in  two  parts,  fastened  together  by  flanges  at  the  center,  as 
shown  in  detail  in  Fig.  12-77.  This  construction  makes  the  outer 
wall  independent  of  the  cylinder  wall  proper,  and  avoids  tempera- 
ture stresses.  The  valve  chambers  are  cast  integral  with  the 
cylinder  casting.  The  cylinder  heads  are  plain  jacketed  covers 
containing  nothing  but  the  stuffing-boxes.  For  the  purpose  of 
safety  against  leakage,  however,  each  head  has  a  double  seat. 
The  front  and  rear  cylinders  are  connected  by  a  distance  piece  of 
box-section,  which  has  large  openings  in  the  side  through  which 
heads  and  pistons  may  be  removed  if  required.  The  pistons  are 


332 


INTERNAL  COMBUSTION  ENGINES 


MODERN   TYPES  OF  COMBUSTION  ENGINES        333 

made  in  two  parts  bolted  together.  These  pistons,  together  with 
their  rods,  are  of  course  water-cooled,  the  water  entering  at  the 
front  cross-head  and  leaving  at  the  tail  cross-head. 

The  distinguishing  feature  of  these  engines,  however,  is  the 
valve  construction,  shown  in  detail  in  Fig.  12-76.  Mr.  Poole,  in 
the  article  mentioned,  describes  the  gear  as  follows: 

"The  cam  shafts  which  drive  the  valve  gear  are  driven  by 
steel  gears,  bevel  gears  being  used  on  the  main  shaft,  driving  back 
through  spur  wheels  to  secure  the  proper  reduction  in  speed  of 
two  to  one.  The  igniters  and  lubricators  are  also  driven  from 
the  cam  shafts,  as  are  also  the  starting  valves,  which  admit  com- 
pressed air  on  the  cylinders  for  starting.  The  inlet  and  exhaust 


FIG.  12-75. 

valves  are  driven  by  cams  made  of  chilled  cast  iron,  located  on 
the  cam  shafts,  which  run  in  bearings  bolted  to  the  side  of  the 
valve  chambers. 

"The  inlet  and  exhaust  valves  are  of  the  unbalanced  mush- 
room type,  working  in  cages  secured  to  the  top  and  bottom  of  the 
valve  chamber.  Both  valves  and  their  cages  are  water-jacketed, 
in  order  to  prevent  back-firing  or  pre-ignitions  on  account  of  the 
treacherous  nature  of  the  gas  used.  Each  inlet  valve  is  com- 
bined with  a  combination  mixing  and  throttling  valve,  of  piston 
form,  so  designed  that  when  the  inlet  valve  opens  gas  and  air 
ports  in  proper  proportion  are  open  for  the  passage  of  gas  and 
air  in  the  ratio  desired,  the  amount  of  the  opening  of  both  being 
fixed  by  the  governor.  From  this  it  will  be  evident  that  the 
engines  operate  with  variable  compression  and  constant  mixture, 
the  supply  of  air  and  gas  to  each  end  of  each  cylinder  being 
throttled  directly  at  each  inlet  valve  for  its  end  of  its  cylinder. 


334 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES        335 


"The  exhaust  valves  are  of  cast  iron  with  nickel-steel  stems 
and  are  thoroughly  water-jacketed,  the  water  being  fed  to  and 
carried  from  the  valve  by  positive  circulation.  The  connection 
of  the  exhaust  valve  cages  with  the  exhaust  pipe  is  so  made  that 
the  cages  can  be  readily  removed  without  disconnecting  any  other 
part  of  the  engine." 

In  discussing  the  reasons  for  locating  the  valves  at  the  side, 
Mr.  Poole  quotes  the  builders  as  follows: 

"It  permits  of  the  use  of  an  absolutely  continuous  bedplate 
under  all  cylinders,  which  is  considered  essential  on  engines  as 
long  as  these  for  maintaining  absolute  alignment  and  permit- 
ting unrestricted  movement  to 
compensate  for  variations  in 
temperature  in  cylinder  walls 
and  connecting  parts. 

"A  solid,  unbroken  founda- 
tion from  one  end  of  the  engine 
to  the  other  is  thus  secured, 
,and  the  builders  consider  that 
a  solid,  unbroken  foundation  is 
more  essential  for  a  gas  engine 
than  for  any  other  prime  mover 
on  account  of  the  enormous 
weight  of  the  reciprocating  parts  and  the  inability  to  fully  coun- 
terbalance. 

"It  enables  all  working  parts  of  the  engine,  without  exception, 
to  be  located  above  the  engine-room  floor  and  therefore  to  be  in 
full  view  of  the  attendants  at  all  times. 

"Inlet-  and  exhaust-valve  driving  motions  from  the  cam 
shaft  are  short  and  direct. 

"Exhaust  valves  are  much  more  accessible  for  removal  when 
located  in  a  valve  chamber  on  the  side,  since  the  crane  can  be 
used  throughout  the  entire  operation  and  all  work  in  connection 
with  the  removal  and  displacement  of  the  exhaust  valves  is  done 
from  the  engine-room  floor. 

"With  valves  located  in  a  side  valve  chamber,  broken  inlet 
and  exhaust  valves  cannot  get  into  the  interior  of  the  cylinder 
and  lodge  between  the  piston  and  the  cylinder-head,  causing 
wrecks. 


FIG.  12-77.  —  Cylinder  Construction, 
Snow  Type  A  Gas  Engine. 


336  INTERNAL  COMBUSTION   ENGINES 

"It  has  been  very  generally  the  opinion  of  gas-engine  designers 
that  the  location  of  the  valves  in  a  side  valve  chamber  of  the 
kind  used  on  the  California  engines  entailed  the  certain  disadvan- 
tage that  foreign  material  entering  the  cylinder  with  the  air  and 
gas  would  deposit  on  the  bottom  of  the  cylinder  counterbore, 
while  if  the  exhaust  valve  be  located  on  the  bottom,  such  deposits 
will  be  carried  out  through  that  valve;  furthermore,  that 
lubricating  oil  collects  in  the  bottom  of  the  counterbore  and  is 
carbonized,  causing  back-firing  and  pre-ignitions.  Experience 
with  these  engines  thus  far  indicates  that  if  lubrication  is  properly 
effected  no  carbonized  oil  is  found  in  the  cylinder,  and  that  when 
oil  is  supplied  excessively  the  resulting  deposit  of  carbon  is  located 
not  on  the  surface  of  the  clearance  space,  but  on  the  top  of  the 
piston  barrel  directly  under  the  oil-inlet  holes,  on  the  piston  rod 
where  it  wipes  in  from  metallic  packing,  and  on  the  face  of  the 
cylinder  head  directly  under  and  close  to  the  piston-rod  hole 
in  the  head." 

The  Cockerill  Engine.  —  This  machine  is  built  by  the  Soc. 
Anon.  John  Cockerill  in  Seraing,  Belgium.  This  firm  builds 
several  types  of  engines,  differing  among  themselves  mainly 
in  their  valve  constructions.  Fig.  12-78*  shows  a  1200.  horse- 
power tandem  gas  engine,  in  which  the  inlet  valve  is  on  top,  the 
exhaust  valve  on  the  bottom  of  the  cylinder.  Both  are  operated 
apparently  from  the  same  cam  on  the  lay  shaft.  This  type  of 
machine  is  built  either  for  quality  or  quantity  governing,  in 
which  case  the  construction  of  the  inlet  valve  differs.  Fig.  12-79 
shows  another  form,  a  single-cylinder  double-acting  engine  direct 
connected  to  a  blowing  cylinder.  The  details  of  the  valve  gear 
of  this  machine  are  quite  clearly  shown  in  Fig.  12-SO.f  Both 
inlet  and  outlet  valves  are  side  by  side  at  the  bottom  of  the  cyl- 
inder. 

Figure  12-81  shows  the  latest  form  of  the  double-acting  tan- 
dem Cockerill  engine. J  The  distinctive  features  of  this  machine 
are  that  all  valves  are  placed  below  the  cylinder  and  that  eccen- 
trics only  are  used  for  operating  these  valves.  The  valve  gear 
proper  represents  one  of  the  most  complicated  constructions  used 

*H.  Dubbel,  Z.  d.  V.  d.  I.,  Sept.,  1905. 
fGiildner,  p.  479. 
JGuldner,  p.  481. 


MODERN   TYPES  Of  COMBUSTION  ENGINES         337 


FIG.  12-78. 


FIG,  12-79. 


338 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES         339 

to-day  and  is  shown  in  section  in  Fig.  12-82.  In  this  figure  at 
the  left,  the  eccentric,  through  its  rod  a  and  the  lever  b,  operates 
the  cam  c  which  positively  opens  and  closes  the  exhaust  valve 
through  the  triple  lever  d.  The  inlet  valve  eccentric,  Fig.  12-82, 
at  the  right,  in  a  similar  manner  operates  the  gas  valve  cam  c 
and  the  inlet  cam  c'.  The  lever  b  actuating  the  gas  valve  cam 
is  disengaged  from  the  rod  a  when  the  trip  arrangement  /-/'  is 
brought  into  play  by  the  cam  disc  e.  The  position  of  this  disc 
on  its  shaft  is  regulated  by  the  governor,  through  the  linkage 
shown,  thus  effecting  speed  regulation.  The  dash  pot  h  allows 
the  gas  valve  to  seat  noiselessly  after  its  linkage  is  released. 


FIG.  12-81.  —  Cockerill  Double-acting  Tandem  Engine 

The  Cockerill  engine  has  found  considerable  application  in 
Europe,  there  being  about  80,000  B.  H.  P.  in  operation  in  121 
engines,  ranging  from  200  to  3000  B.  H.  P.  The  fuel  used  is 
mainly  blast  furnace  gas. 

The  Niirnberg  Engine.  —  Although  the  Allis-Chalmers  Company 
of  Milwaukee  have  been  the  American  licensees  of  the  Maschinen- 
Gesellschaft  Niirnberg,  makers  of  the  Niirnberg  engine,  the  large 
gas  engine  now  turned  out  by  the  American  firm,  differs  in  some 
of  the  important  details  from  the  original  German  design. 

The  Niirnberg  engine  is  to-day  perhaps  the  most  important 
four-cycle  gas  engine  built  in  Germany,  and  for  that  reason  a 
description  is  first  given  of  the  German  machine,  to  be  followed 
by  a  few  details  of  the  Allis-Chalmers  engine  as  far  as  they  could 
be  obtained. 


340 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES        341 

All  of  the  medium  sized  and  large  Niirnberg  engines  are  double- 
acting,  either  single-cylinder  or  tandem.  They  range  in  size 
from  250  to  6000  horse-power,  the  larger  powers  being  the  twin- 
tandem  type.  Probably  the  best  description  ever  given  of  this 
machine  is  contained  in  Riedler's  "  Gross  Gasmaschinen,"  from 
which  the  cross-section,  Fig.  12-83,  together  with  the  two  follow- 
ing figures,  is  taken.  This  cut  shows  frame,  cylinder,  and  valve 
construction  very  clearly.  The  only  part  rigidly  fastened  to  the 
foundation  is  the  main  frame,  which  is  of  the  center  crank  type, 
as  preferred  by  all  European  builders.  The  cylinders  rest  on 
supports  such  that  they  can  freely  expand  and  contract  under 
temperature  changes.  The  gas  and  inlet  valves  are  placed  on 
top  and  the  exhaust  valve  at  the  bottom  of  the  cylinder.  The 
inlet  and  exhaust  ports  are  cast  in  one  part  with  the  cylinder  and 
jacket  walls.  This  reduces  the  cylinder  heads  to  simple  water- 
jacketed  covers,  a  point  of  great  advantage  as  compared  with  the 
^complicated  cylinder  heads  of  former  days.  All  valve  cages  with 
their  valves  are  easily  removable  for  inspection.  The  exhaust 
valves  are  water-cooled.  The  valves  are  operated  from  a  lay 
shaft  running  alongside,  Fig.  12-84,  by  means  of  eccentrics  and 
not  by  cams.  How  this  motion  is  transmitted  to  the  valve  stems 
by  roller  levers  to  avoid  shock  and  noise  is  very  clearly  shown 
in  Fig.  12-85.  The  pistons  are  as  simple  as  those  of  a  steam 
engine.  The  method  of  fastening  them  on  the  shaft  together  with 
the  water-cooling  arrangements  for  rods  and  pistons  are  indi- 
cated in  Fig.  18-83.  The  weight  of  piston  and  rod  is  carried  by 
outside  bearings,  which  relieves  both  cylinder  and  stuffing-boxes. 

The  greatest  attention  to  accessibility  has  been  paid  in  the 
design  of  this  engine.  As  shown  in  Fig.  12-86,  by  disconnecting 
the  piston  rod  between  the  cylinders,  disconnecting  the  connect- 
ing rod  and  sliding  the  rod  and  cross-head  forward,  and  by  talking 
off  the  front  and  rear  cylinder  covers,  the  entire  engine  interior  is 
at  once  open  to  inspection. 

The  Niirnberg  engine  regulates  by  pure  quality  regulation, 
that  is,  the  amount  of  gas  only  is  cut  down  as  the  load  drops. 
To  accomplish  this  there  is  a  gas  valve  placed  ahead  of  each  main 
inlet  valve  on  the  top  of  the  cylinder.  Fig.  12-83  shows  the  con- 
struction of  these  valves  in  section  and  the  method  of  operating 
them  by  eccentrics  from  the  lay  shaft  may  be  seen  in  Fig.  12-84. 


342 


INTERNAL  COMBUSTION  ENGINES 


MODERN   TYPES  OF  COMBUSTION  ENGINES        343 


FIG.  12-84.  —  Niirnberg  Double-acting  Tandem  Engine. 


FIG.  12-85.  —  Details  of  'Valve  Gear,  Niirnberg  Engine. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        345 

The  latter  illustration  also  shows  the  centrifugal  governor  and 
the  governor  shaft  running  alongside  of  the  cylinders.  From  this 
governor  shaft  reach  rods  run  to  the  gas  valves  and  control  the 
time  of  the  opening  of  these  valves  in  the  manner  explained  in 
Chapter  XIV.  In  some  of  the  later  engines  the  details  of  the 
governor  mechanism  are  changed  somewhat  *  but  the  principle 
of  operation  is  the  same  in  all,  i.e.,  to  open  the  gas  valve  later  in 
the  stroke  as  the  load  drops  and  to  keep  the  time  of  closure  the 
same.  The  air  is  not  throttled  at  any  time,  hence  the  compres- 
sion remains  about  the  same.  It  is  interesting  to  trace  out  the 
sequence  of  events  in  a  four-cycle  tandem  engine,  for  which  pur- 
pose Fig.  12-87  published  by  the  Allis-Chalmers  Company  is  given. 

SEQUENCE  OF  OPERATIONS  IN 

THE  FOUR-CYCLE.  DOUBLE-ACTING  SYSTEMl 

TANDEM  OR  TWIN  TYPE. 


POWER 

Exhaust  POWER 

Suction  Exhaus 

Compression  Suction 


POWER 

4  POWER  STROKES  IN  2  REVOLUTIONS. 
FIG.  12-87. 

Most  Niirnberg  engines  operate  on  blast  furnace  gas.  The 
table  on  page  346,  also  from  the  catalogue  of  the  Allis-Chalmers 
Company,  will  serve  to  give  some  idea  of  the  cylinder  sizes,  speeds, 
floor-space,  etc. 

It  has  already  been  mentioned  that  the  engine  now  built  by 
the  Allis-Chalmers  Company  is  not  quite  like  the  Niirnberg  ma- 
chine. The  following  is  a  description  of  one  of  these  engines,  as 
given  in  Power,  January  21,  1908.  The  engine,  Fig.  12-88  is  of 
the  twin-tandem,  double-acting  type  and  direct  connected  to  a 
1040  K.W.  Crocker- Wheeler  generator: 

"It  is  of  the  side-crank  type  so  generally  used  in  steam  engine 

*  See  Zeitschrift  des  Vereins  deutscher  Ingenieure,  Aug.  11,  1906,  and  Sept. 
22,  1906. 


346 


INTERNAL  COMBUSTION  ENGINES 


construction.  The  pistons  are  supported  entirely  by  the  piston 
rods,  which  are  turned  with  sufficient  camber  to  make  them  dead 
straight  when  the  weight  of  the  pistons  is  put  on  them.  The 
rods  are  equipped  with  intermediate  and  tail  shoes,  as  usual  with 
large  tandem  construction,  running  on  guides  between  the  cylin- 
ders and  behind  the  rear  cylinder,  in  addition  to  the  main  cross- 
head. 

NURNBERG  GAS  ENGINE 
TABLE  OF  STANDARD  SIZES 


TANDEM 

TWIN 

| 

TWIN-TANDEM 

Size  of 

Floor 

Size  of 

Floor 

Size  of 

(3 

Floor 

Cylinders 

1 

Space 

Cylinders 

1 

Space 

Cylinders 

Space 

1 

RH 

a 

P^ 

& 

PH 

PC 

H  "& 

1 

K 

«| 

H 

fi 

w 

"c  £ 

1 

.2 

pq 

W^ 

to 

pa 

(LI 

O 

PQ 

Wfc 

1 

1 

1 

| 

s| 

1 

1 

J 

1 

i 

•1 

1 

I 

1 

3 
1 

| 

ed  *"ctf 

1 

I"H 

(S 

*0 

0 

M 

<A 

PH 

0 

0 

£ 

"o 

6 

G 

cS 

3 

1 

1 

1 
£ 

!~° 

£j 

1 

1 

i 

ua 

1 

c"o 

1 

ti 

£ 

03 

b 

1 

1 
Cfl 

1 

P 

.£ 

18 

24 

150 

260 

29 

11      18 

24 

150 

245 

19 

17 

18 

24 

150 

520 

29 

17 

20 

24 

150 

320 

29 

11      20 

24 

150 

305 

19 

17 

20 

24 

150 

640 

29 

17 

21 

30 

125 

370 

33 

13     21 

30 

125 

350 

22 

20 

21 

30 

125 

740 

33 

20 

22 

30 

125 

405 

33 

13     22 

30 

125 

385 

22 

20 

22 

30 

125 

810 

33 

20 

24 

30 

125 

490 

33 

13     24 

30 

125 

465 

22 

20 

24 

30 

125 

980 

33 

20 

24 

36 

115 

545 

38 

15     24 

36 

115 

515 

25 

23 

24 

36 

115 

1090 

38 

23 

26 

36 

115 

630 

38 

15     26 

36 

115 

600 

25 

23 

26 

36 

115 

1260 

38 

23 

28 

36 

115 

740 

38 

15     28 

36 

115 

700 

25 

23 

28 

36 

115 

1480 

38 

23 

30 

42 

100 

855 

44 

m  30 

42 

100 

810 

29 

27 

30 

42 

100 

1710 

44 

27 

32 

42 

100 

985 

44 

17*   32 

42 

100 

935 

29 

27 

32 

42 

100 

1970 

44 

27 

34 

42 

100 

1105 

44 

17i    34 

42 

100 

1050 

29 

27 

34 

42 

100 

2210 

44 

27 

36 

48 

92 

1300 

50 

21     36 

48 

92 

1240 

33 

32 

36 

48 

92 

2600 

50 

32 

38 

48 

92 

1460 

50 

21     38 

48 

92 

1400 

33 

32 

38 

48 

92 

2920 

50 

32 

40 

48 

92 

1630 

50 

21 

40 

48 

92 

1550 

33 

32 

40 

48 

92 

3260 

50 

32 

42 

54 

86 

1875 

60 

26 

42 

54 

86 

1780 

40 

38 

42 

54 

86 

3750 

60 

38 

44 

54 

86 

2080 

60 

26     44 

54 

86 

1980 

40 

38 

44 

54 

86 

4160 

60 

38 

46 

54 

86 

2280 

60 

26 

46 

54 

86 

2170 

40 

38 

46 

54 

86 

4560 

60 

38 

48 

60 

78 

2475 

70 

30 

48 

60 

78 

2350 

45 

44 

48 

60 

78 

4950 

70 

44 

50 

60 

78 

2720 

70 

30  1  50 

60 

78 

2580 

45 

44 

50 

60 

78 

5440 

70 

44 

52 

60 

78 

2950 

70 

30     52 

60 

78 

2800 

45 

44 

52 

60 

78 

5900 

70 

44 

NOTE  —  The  overall  widths  given  in  the  above  tables  allow  for  a  plain  fly-wheel: 
propei*  addition  must  be  made  if  a  band-wheel  is  substituted  or  an  electric  generator 
direct  connected  upon  the  crank-shaft. 

"  There  are  two  inlet  valves  to  each  combustion  chamber,  one 
for  air  and  one  for  gas,  but  both  are  mounted  in  a  single  cage. 
The  air  valve  is  of  the  piston  type  and  the  gas  valve  is  of  the 
poppet  type,  its  axis  being  in  line  with  that  of  the  air  valve. 
The  latter  is  opened  at  the  beginning  of  the  suction  stroke  and 


MODERN  TYPES  OF  COMBUSTION  ENGINES        347 

« 

kept  open  throughout  that  stroke.  The  gas  valve,  however,  is 
open  during  varying  proportions  of  the  suction  stroke,  according 
to  the  requirements  of  the  load.  The  engine,  therefore,  operates 
with  constant  compression  and  varying  mixture  proportions. 
The  compression  pressure  is  about  180  pounds  per  square  inch, 
absolute. 

"  The  ignition  is  by  make-and-break  mechanism  electrically 
operated;  that  is,  the  movable  electrode  is  rocked  by  means  of  an 
electromagnet  and  the  latter  is  energized  by  the  ignition  current 
controlled  by  a  'timer'  or  so-called  commutator  driven  synchro- 


FIG.  12-88.  —  Allis-Chalmers  Double-acting  Twin  Tandem  Engine. 

nously  with  the  cam  shaft.  Tell-tale  incandescent  lamps  are 
connected  in  circuit  with  the  igniter  magnets  and  indicate  the 
performance  or  default." 

The  main  differences  between  this  and  the  Niirnberg  engine 
then  appear  to  be  different  cylinder  supports,  the  combination  of 
the  gas  and  inlet  valves  in  one  housing,  and  the  use  of  the  side- 
crank  frame. 

Premier    Engine.  —  Probably    the    best    description    of    this 
engine  is  found  in  Robinson's  "Gas  and  Petroleum  Engines."     It 
is  of  what  is  known  as  the  positive  scavenger  type,  i.e.,  the  com-, 
bustion  chamber  is  thoroughly  washed  out  with  air  before  a  new 
charge  is  admitted.     The  cylinder  is  single-acting,  and  single- 


348  INTERNAL  COMBUSTION  ENGINES 

cylinder  and  tandem  units  are  built.  The  former  go  up  to  250 
horse-power,  the  latter  up  to  1200  horse-power.  The  pump 
serving  to  furnish  the  air  for  scavenging  is  usually  placed  ahead 
of  the  first  power  cylinder,  but  in  some  of  the  later  designs  the  air 
pump  is  placed  obliquely  above  the  first  cylinder. 

Figures  12-89  and  12-90  are  two  illustrations  from  Robinson. 
The  first  shows  the  general  appearance  of  the  machine,  the  method 
of  operating  the  inlet  and  exhaust  valves  from  the  lay  shaft,  the 
oblique  rod  to  operate  the  air-pump  valve,  and  the  governor 
details.  The  second  shows  several  sectional  views  from  which 
the  operation  may  be  explained.  The  piston  D  of  the  single- 
acting  air  pump  is  rigidly  connected  to  the  piston  C  of  the  first 
power  cylinder.  The  second  power  piston  is  connected  by  means 
of  the  yoke  K  and  the  side  rods  R  R  to  the  air  pump  piston. 
Thus  the  use  of  a  stuffing-box  in  the  combustion  chamber  of  the 
forward  power  piston  is  avoided.  H  H  are  the  combination  air 
and  gas  inlet  valves,  and  G  G  the  exhaust  valves,  operated  as 
shown  in  the  transverse  cross-section. 

The  operation  is  as  follows:  On  the  out  stroke,  air  is  admitted 
to  the  air  pump  D  through  the  grid  valve  F,  shown  in  the  section 
X  X.  On  the  return  stroke  this  air  is  compressed  into  the  passage 
D-E,  and  serves  to  scavenge  out  the  power  cylinder  just  exhaust- 
ing when  the  inlet  valve  H  into  that  cylinder  is  opened  about  one- 
half  exhaust  stroke.  On  the  next  out  stroke  the  air  pump  takes  a 
new  charge,  but  at  the  same  time  the  valve  F  has  also  opened 
communication  to  the  passage  E,  so  that  the  cylinder  just  charg- 
ing may  draw  air  freely.  Above  the  inlet  valve  //  there  is  placed 
a  cylindrical  valve,  which  during  the  scavenging  action  opens  the 
air  ports  completely  and  keeps  the  gas  ports  closed,  but  which, 
at  the  beginning  of  the  charging  stroke,  shifts  its  position  to  give 
the  proper  relation  between  air  and  gas.  While  the  exhaust  and 
charging  strokes  above  described  take  place  in  one,  say  the  first, 
cylinder,  the  second  has  completed  its  compression  and  expansion 
strokes.  On  the  third  (the  in  stroke)  of  the  pump,  therefore,  we 
shall  have  compression  in  the  first  cylinder  and  exhaust  in  the 
second.  The  pump  then  scavenges  out  the  second  cylinder  dur- 
ing the  last  half  of  its  exhaust  stroke. 

Speed  regulation  in  this  engine  is  effected  by  the  governor 
cutting  out  the  gas  from  the  back  cylinder  altogether  below  a 


MODERN  TYPES  OF  COMBUSTION  ENGINES        349 


350 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES        351 

certain  load.  Above  this  a  charge  of  gas  is  admitted  occasion- 
ally, while  above  half  power  both  cylinders  work  practically 
continuously. 

Robinson  states  that  the  tandem  design  and  the  positive 
scavenging  action  make  the  Premier  engine  well  adapted  for  the 
burning  of  cheap  fuel  gas.  Giildner  judges,  from  the  high  effi- 
ciencies obtained  in  conjunction  with  mean  effective  pressures 
exceeding  110  pounds  per  square  inch,  that  the  combustion  process 
in  this  engine  must  be  very  perfect. 

The  Deutz  Engine.  —  The  Deutz  Company  of  Deutz-Cologne 
were  the  first  firm  to  build  Otto  engines  and  they  have  from  the 
first  been  prominently  identified  with  the  development  of  this 
type  of  engine.  Their  present-day  constructions  embrace  several 
designs  of  excellent  form. 

The  large  engines  are  all  double-acting  and  are  made  either 
single-cylinder,  twin  or  tandem.  The  general  features  of  the  de- 
sign of  a  600  B.  H.  P.  twin  engine  are  shown  in  longitudinal  cross- 
section  in  Fig.  12-91  and  in  transverse  section  in  Fig.  12-92.* 
The  cylinder  differs  from  that  of  the  Nurnberg  engine  in  that  the 
jacket  wall  is  not  continuous.  This  is  done,  of  course,  to  prevent 
temperature  stresses.  The  central  space  is  closed  by  a  saddle 
casting  as  shown.  Inlet  and  exhaust  valves  are  placed  in  separate 
cages  easily  removable.  The  details  of  piston  design  and  the 
water-cooling  arrangements  are  clearly  indicated.  The  manner  of 
operating  the  valves  from  the  lay  shaft  is  shown  in  Fig.  12-92. 
All  Deutz  engines  govern  by  throttling  a  mixture  of  constant 
composition.  In  the  particular  engine  under  discussion  the 
throttle  valve  is  a  multi-ported  cylinder  surrounding  the  inlet 
valve  stem.  It  is  so  designed  as  to  keep  the  ratio  of  gas  to  air 
the  same  as  that  set  by  the  hand-operated  valves  shown  in  the  gas 
and  air  passages,  but  depending  on  the  load,  the  mixture  is 
throttled  more  or  less.  How  the  movement  of  the  valve  is  con- 
trolled by  varying  the  position  of  the  fulcrum  about  which  the 
throttle  valve  lever  turns  can  be  easily  traced  out  by  following 
the  governor  linkage. 

The  arrangement  of  the  throttle  valve  is  somewhat  different 
in  smaller  engines.  Thus  in  the  250  B.  H.  P.  engine,  a  cross- 
section  of  which  is  shown  in  Fig.  12-93,  the  throttle  valve  is 
*  From  H.  Dubbel,  Zeitschrift  d.  V.  d.  I.,  Sept.  2,  1905. 


352 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES        353 


354 


INTERNAL  COMBUSTION  ENGINES 


FIG.  12-93.  —  Valve  Gear  Details,  250  B.  H.  P.  Deutz  Engine. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        355 

independent  of  the  main  inlet  valve.  The  governing  features, 
however,  are  quite  similar. 

The  Oechelhduser  Engine.  —  The  Oechelhauser  Engine,  built 
by  several  firms  in  Germany,  is  a  two-cycle  machine  of  distinctive 
design,  as  may  be  seen  from  the  cross-sections,  Figs.  12-94,  which 
represents  a  1000  horse-power  machine  built  by  A.  Borsig.* 

The  power  cylinder  is  open  at  both  ends  and  contains  two 
single-acting  pistons.  The  front  piston  is  connected  to  the 
middle  crank  of  a  three-throw  crank  shaft  by  piston  and  connect- 
ing rod  in  the  ordinary  manner.  The  rod  of  the  back  piston  is 
fastened  to  a  yoke  which  transmits  the  motion  through  rods  on 
each  side  of  the  cylinder  to  cross-heads  and  connecting  rods 
working  on  the  two  outside  crank  pins.  This  construction, 
while  complex  and  probably  costly,  results  in  almost  perfect 
balance.  There  are  no  valves  as  such.  The  exhaust  gases  escape 
through  a  ring  of  ports  which  is  uncovered  by  the  front  piston 
near  the  end  of  the  out  stroke.  Similarly  the  back  piston  near  the 
end  of  its  out  stroke  uncovers  first  a  ring  of  ports  admitting  a 
charge  of  air  for  scavenging,  and  a  moment  later  the  gas  or  mix- 
ture ports.  On  the  return  stroke  these  rings  of  ports  are  covered 
one  after  the  other  and  compression  ensues  between  the  two 
pistons.  When  in  their  inner  dead  center  position,  ignition  is 
made  to  take  place  electrically,  and  the  pistons  are  driven  apart 
on  their  power  strokes. 

Gas  and  air  under  certain  small  pressures  are  furnished  to 
the  receivers  surrounding  the  inlet  ports  by  means  of  a  combina- 
tion air  and  gas  pump  which  is  usually  operated  by  a  tail  rod.  In 
blowing  engines  the  blowing  cylinder  is  usually  so  connected,  and 
the  air  and  gas  pump  is  then  placed  under  floor. 

At  full  load  the  mixture  follows  the  preliminary  charge  of 
pure  air  used  for  scavenging  to  about  three-quarters  or  seven- 
eighths  of  the  stroke.  Regulation  is  effected  by  controlling  the 
amount  of  mixture  admitted  to  the  cylinder.  The  means  for 
doing  this  are  discussed  in  Chapter  XIV. 

Oechelhauser  engines  have  given  good  satisfaction  on  blast- 
furnace and  coke-oven  gas.  The  general  appearance  of  a  twin 
engine  of  this  type  is  shown  in  Fig.  12-95. 

*  Hoffman,  Zeitschrift  d.  V.  d.  I.,  Sept.  15,  1906. 


356 


INTERNAL  COMBUSTION  ENGINES 


MODERN  TYPES  OF  COMBUSTION  ENGINES        357 


358  INTERNAL  COMBUSTION  ENGINES 

B.  Liquid  Fuel  Engines 

3.  GASOLINE  ENGINES.  —  The  very  great  majority  of  all  port- 
able internal  combustion  engines  are  gasoline  engines,  and  the 
same  is  true  of  a  large  percentage  of  stationary  internal  combus- 
tion engines  for  small  powers.  We  may  thus  divide  all  gasoline 
engines  into  three  classes  —  stationary  engines,  marine  engines, 
and  automobile  engines.  The  number  of  firms  engaged  in  the 
manufacture  of  these  engines  is  very  large.  Usually  the  various 
makes  differ  only  in  minor  detail,  and  for  that  reason  only  one 
or  two  type  examples  under  each  class  will  be  considered. 

Stationary  Gasoline  Engines.  —  The  general  type  of  this 
machine  either  vertical  or  horizontal  does  not  differ  much  from 
that  of  the  small-powered  stationary  gas  engine,  several  makes  of 
which  have  already  been  discussed.  It  is  usually  possible  to  con- 
vert any  gas  engine  of  this  type  into  a  gasoline  engine  by  the  simple 
addition  of  a  carbureting  device.  A  number  of  the  latter  have 
been  described  in  Chapter  VIII. 

The  Foos  Gasoline  Engine.  —  This  machine  is  made  by  the 
Foos  Gas  Engine  Company  of  Springfield,  Ohio.  The  cylinder, 
Fig.  12-96,  is  partly  supported  by  the  frame,  making  an  especially 
rigid  construction.  The  cylinder  head  is  a  plain  flat  cover.  Both 
valves,  which  are  of  the  poppet  type,  work  upward  and  are  me- 
chanically operated;  they  are  not  affected  by  any  governor  action. 
Thus  if  the  governor  keeps  the  fuel  valve  closed,  pure  air  is 
worked  through  the  engine,  cooling  the  cylinder  and  clearing  it 
thoroughly  from  burned  gases.  The  valves  are  operated  by  bell 
cranks  and  rods  as  shown.  These  rods  are  in  turn  actuated  by 
cams  on  the  shaft  of  the  secondary  gear,  A,  Fig.  12-96.  The 
valves  have  their  seat  castings  separate  from  the  cylinde'r,  but  in 
order  to  remove  the  valves  for  inspection  or  regrinding  it  is  nec- 
essary only  to  remove  the  plugs  in  the  top  of  the  valve  cages.  In 
Fig.  12-96,  B  is  the  rod  operating  the  fuel  valve,  C  the  fuel  pump, 
and  D  the  igniter  rod.  The  fuel  may  be  gasoline,  naphtha,  or 
distillate. 

Foos  engines  are  governed  on  the  hit-and-miss  principle.  In 
Fig.  12-97,  E  is  the  igniter  rod,  C  the  fuel  valve  lever  which  is 
oscillated  by  a  cam  on  the  shaft  of  the  secondary  gear  G.  This 
gear,  through  a  pinion,  also  drives  the  governor  D.  The  latter  is 


MODERN  TYPES  OF  COMBUSTION  ENGINES        359 


FIG.  12-96.  —  Foos  Gasoline  Engine. 


FIG.  12-97.  —  Governing  Details,  Foos  Engine. 


360 


INTERNAL  COMBUSTION  ENGINES 


of  the  fly-ball  type,  and,  when  the  speed  becomes  excessive,  pulls 
the  block  B,  on  the  lower  end  of  the  governor  lever  A,  out  of  line 
with  the  blade  F.     Thus  F  misses  the  fuel  valve  rod  and  the  en- 
gine  fails  to   receive    a    charge. 
The  speed  of  the  engine  may  be 
adjusted     during    operation    by 
varying  the  position  of  the  ful- 
crum A  by  turning  the  nut  H. 

In  place  of  the  ordinary  ham- 
mer break  system,  a  wipe  spark 
igniter  is  employed.  In  Fig. 
12-98,  the  revolving  electrode, 
every  second  turn  of  the  engine, 
wipes  over  and  snaps  off  the  in- 
sulated electrode.  Thus  the 
points  of  contact  are  always 
kept  clean  and  bright.  The  igniter  is  placed  directly  over  the 
inlet  valve  to  insure  a  good  combustible  mixture. 

The  Olds  Gasoline  Engine.  —  Fig.  12-99  shows  the  carbureter 


FIG.  12-98.  —  Wipe  Spark  Igniter, 
Foos  Engine. 


FIG.  12-99. 


)lds  Gasoline  Engine. 


side  and  Fig.  12-100  the  valve  construction  of  the  Olds  Type  A 
gasoline  engine.     This  is  an  engine  of  very  simple  design.     Both 


MODERN  TYPES  OF  COMBUSTION  ENGINES        361 

valves  are  of  the  poppet  type,  the  upper,  the  inlet  valve,  being 
automatic  while  the  exhaust  valve  is  operated  by  bell  crank  and 
push  rod.  The  latter  is  actuated  by  a  cam.  Fig.  12-99  shows  the 
carbureter  and  its  adjusting  valve.  Until  recently  the  gasoline 
was  fed  to  the  carbureter  from  a  small  reservoir  kept  filled  to  a 
certain  level  by  a  small  plunger  pump  driven  from  the  shaft.  In 
some  of  the  recent  designs  this  pump  has  been  eliminated,  the 
carbureter  getting  fuel  by  simple  suction  feed. 


FIG.  12-100.  —  Olds  Gasoline  Engine. 

The  governor,  which  is  of  the  fly-wheel  type,  is  shown  in  Fig. 
12-100.  It  operates  to  keep  the  exhaust  valve  open  when  the 
speed  exceeds  the  normal,  at  the  same  time  locking  the  inlet 
valve,  so  that  no  charge  can  enter  the  cylinder.  The  governor 
may  be  adjusted  to  give  speeds  varying  from  200  to  600,  and  a 
change  of  about  50  turns  per  minute  may  be  made  while  the  en- 
gine is  in  operation. 

The  jump  spark  ignition  system  is  used,  which  is  unusual  in 
small  stationary  engines.  The  governor  serves  also  to  throw 
the  commutator  of  the  system  out  of  action  should  the  engine 
fail  to  take  a  charge  on  a  miss-stroke. 

Type  A  Olds  gasoline  engines  are  built  in  six  sizes  from  3  to  18 
horse-power. 

Marine  Gasoline  Engines,  —  These  engines  are  of  either  the 


362 


INTERNAL  COMBUSTION  ENGINES 


two-  or  four-cycle  type,  but  in  nearly  all  cases  vertical.  The 
maximum  power  developed  in  one  cylinder,  in  the  ordinary  launch 
motor,  is  usually  about  5-8  horse-power,  higher  power  than  this 
being  obtained  by  the  multiplication  of  cylinders. 

Perhaps  the  majority  of  engines  of  this  type,  especially  those 
of  fairly  high  speed,  600  to  800,  are  equipped  with  the  jump  spark 
system;  many  builders,  however,  favor  the  hammer  break  ignition. 


FIG.  12-101.  — Strelinger  Four-cycle  Marine  Engine. 

Small  gasoline  boat  engines  are  very  rarely  fitted  with  gover- 
nor control.  The  speed  is  changed  in  most  cases  with  the  throttle 
or  the  spark,  or  both,  as  in  automobile  engines.  A  favorite  way 
of  checking  the  speed  of  small  boats  is  by  the  use  of  a  reversible 
propeller,  in  which  case  the  speed  of  the  engine  need  not  be 
changed  in  any  way. 

The  following  two  types  of  engines  illustrate  the  general 
features  of  the  four-  and  two-cycle  marine  engines. 

The  Strelinger  Four-cycle  Marine  Gasoline  Engine.  —  A  10 
horse-power  engine  made  by  the  C.  A.  Strelinger  Company  is 
illustrated  in  Fig.  12-101  and  Fig.  12-102.  In  this  design  the 
heads  are  cast  in  one  part  with  the  cylinders.  The  latter  are 
rigidly  bolted  to  the  crank  case  casting.  The  cam  shaft  and  its 
drive  are  enclosed  in  the  crank  case.  The  cams  on  this  shaft 


MODERN  TYPES  OF  COMBUSTION  ENGINES        363 

operate  the  exhaust  valve  and  the  trip  gear  of  the  make-and- 
break  igniter.  By  pushing  in  the  lever,  marked  255  in  Fig.  12-101, 
at  starting,  the  compression  is  partly  relieved  and  the  spark  re- 
tarded on  all  of  the  cylinders,  making  starting  easier.  After  start- 
ing the  lever  is  returned  to  its  former  position.  There  seems  to 
be  no  other  spark  control. 


FIG.  12-102.—  Streling-r  Engine. 

The  inlet  valve  is  automatic.  Above  each  inlet  valve  there 
is  a  throttle  valve  whose  position  is  controlled  by  the  lever  H. 
The  combustible  mixture  is  formed  by  drawing  the  air,  for  the 
purpose  of  warming  it,  from  around  the  exhaust  pipe,  and 
through  the  pipe  X,  Fig.  12-101,  through  the  mixing  valve  B,  Fig. 
12-102.  Here  it  picks  up  a  certain  quantity  of  gasoline,  which  is 
furnished  through  pipe  A  and  the  needle  valve  C,  arid  then  passes 
through  pipe  Y  to  the  cylinders.  Mixing  valve  B  is  automatic, 
adjusting  the  amount  of  gasoline  to  the  amount  of  air  passing. 
The  latter  of  course  depends  upon  the  position  of  the  throttle 
valve  and  the  load  on  the  engine.  The  mixture  is  claimed  to  be 
uniform  through  the  range'  of  speeds. 


364  INTERNAL  COMBUSTION  ENGINES 

The  Lozier  Two-cycle  Marine  Engine.  —  Like  nearly  all  small 
two-cycle  engines,  this  machine  precompresses  the  charge  in  the 
crank  case.  In  Fig.  12-103  *  an  explosion  has  just  taken  place 
above  the  piston.  The  new  charge  of  gasoline  vapor  and  air  has 
just  been  drawn  into  the  crank  case  B  through  the  opening  A 
from  the  carbureter.  The  explosion  forces  the  piston  down  and 
compresses  the  charge  in  B  to  a  pressure  in  the  neighborhood  of 
5  pounds.  Near  the  end  of  the  down  stroke  the  upper  edge  of 
the  piston  uncovers  the  exhaust  port  F,  Fig.  12-104,  and  the 
larger  part  of  the  burned  gases  escape.  A  moment  later  the  inlet 
port  C ',  Fig.  12-105,  is  also  opened,  and  the  new  charge  enters, 
being  deflected  upward  by  the  baffle  G  and  driving  out  the  rest  of 
the  burned  gases.  On  the  next  succeeding  up  stroke  the  piston 
closes  first  the  inlet  port,  next  the  exhaust  port,  and  compression 
commences.  Ignition  takes  place  when  the  igniter  gear  moves 
one  of  the  electrodes^  and  breaks  the  contact  at  E,  Fig.  12-103. 
The  igniter  gear  is  shown  in  detail  in  Fig.  12-106.  Normally  the 
outside  blade  E  which  pivots  about  F  is  held  down  by  the  plun- 
ger Z),  so  that  the  lower  electrode  inside  of  the  cylinder  is  not  in 
contact  with  the  upper.  The  rod  B  is  moved  up  and  down  by  an 
eccentric  on  the  engine  shaft.  On  the  upward  motion  the  plunger 
D  is  forced  upward,  allowing  plunger  M  to  raise  E  so  that  just  be- 
fore the  spark  is  desired  the  electrodes  inside  are  in  contact  and 
the  circuit  is  made.  In  the  meantime  the  point  of  the  adjustable 
screw  J  commences  to  force  the  trigger  C  to  one  side  until,  at  the 
moment  the  spark  is  desired,  the  plunger  D  snaps  off  suddenly, 
breaking  contact  inside  by  forcing  down  the  blade  E. 

The  carbureting  device,  Fig.  12-107,  is  simple  and  effective. 
The  air  is  pre-heated  by  passing  it  around  the  exhaust  pipe. 
Gasoline  enters  at  F,  and  mixes  with  the  air  when  the  inrush  due 
to  the  suction  in  the  crank  case  lifts  the  automatic  valve  B,  flow- 
ing out  from  opening  A  in  the  seat  of  the  valve.  The  dial  D  indi- 
cates the  position  of  the  gasoline  valve. 

The  speed  of  the  engine  is  controlled  by  the  position  of  a  butter- 
fly throttle  valve  in  the  transfer  passage,  as  indicated  in  Fig. 
12-103. 

The  particular  construction  of  the  two-cycle  machine  above 
described  is  known  as  the  two-port  two-cycle.  In  this  type  the 
*  SiWey  College  Thesis  of  Bayne  and  Speiden. 


MODERN  TYPES  OF  COMBUSTION  ENGINES     .   365 


366   .  INTERNAL  COMBUSTION  ENGINES 

port  admitting  the  charge  to  the  crank  case  is  at  no  time  covered 
by  the  piston.  Hence  the  carbureting  device  is  subject  to  the 
pressures  generated  by  possible  explosions  in  the  crank  case, 
and  if  this  is  of  such  type  as  to  be  hurt  by  such  explosion,  it  must 
be  suitably  protected  by  check  valve.  This  difficulty  is  overcome 
by  the  use  of  the  three-port  two-cycle  engine.  This  is  the  type 
of  engine  in  which  the  piston  also  controls  the  inlet  port  into  the 
crank  case,  as  is  clearly  shown  in  Fig.  12-108,  which  illustrates 


FIG.  12-106.  —  Igniter  Gear  Lozier  Two-cycle  Marine 
Engine. 

the  construction  and  operation  of  the  Fairbanks  vertical  Marine 
Engine. 

The  application  of  the  internal  combustion  engine  to  the 
propulsion  of  vessels  other  than  pleasure  launches  is  becoming 
of  more  and  more  importance.  At  the  present  day  several 
rather  small  sized  cargo  boats  and  barges  are  already  fitted  with 
suction  gas  apparatus  and  engines,.  The  question  has  perhaps 
received  the  greatest  amount  of  attention  in  England,  where 


MODERN  TYPES  OF  COMBUSTION  ENGINES        367 


Crossley  Brothers,  Thornycroft,  and  Vickers  Sons  &  Maxim 
have  built  suction  gas  apparatus  for  marine  propulsion.*  In  this 
country  the  Standard  Motor  Construction 
Company  of  Jersey  City  have  lately  turned 
out  a  marine  gas  engine  which  deserves  spe- 
cial attention. 

The  Standard  Marine  Gasoline  Engine. 
-  The  following  description  of  this  engine 
appeared  in  International  Marine  Engineer- 
ing, September,  1907.  The  data  given  refers 
to  the  300  horse-power  engine  of  the  motor 
yacht  Standard,  but  a  500  horse-power  en- 
gine of  the  same  type  for  the  schooner  North- 
land has  already  been  built. 

Figure  12-109  shows  a  cross-section  of 
the  Standard's  engine, and  Fig.  12-110  a  view 
of  the  inlet  side.  The  following  is  the  description  given: 

"  These   engines    have   in   reality   twelve   working   cylinders, 


FIG.  12-107.  —  Carbu- 
reter Lozier  Two-cy- 
cle Marine  Engine. 


FIG.  12-108.  —  Fairbank  Vertical  Three  Port  Two-cycle  Marine  Engine. 

figured  from  the  point  of  view  of  the  usual  construction  of  gas 
engines.     The  result  is  an  extremely  smooth  and  quiet  running 

*  See  an  interesting  article  hy  A.  V.  Coster  on  "  Gas  Power  on  Shipboard," 
in  Gassier 's  Magazine,  November,  1907. 


368 


INTERNAL  COMBUSTION  ENGINES 


FIG.  12-109.  —  Cross-section  of  300  H.P.  Standard 
Marine  Gasoline  Engine. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        369 


370  INTERNAL  COMBUSTION  ENGINES 

machine,  well  balanced,  and  with  the  valves  so  arranged  that 
practically  the  only  vibration  noticeable  is  occasioned  by  the 
force  feed  oil  pumps,  which  give  individual  feed  to  every  cylinder 
and  bearing.  Ignition  is  of  the  make-and-break  type,  while 
pistons  and  piston  rods  are  water-cooled,  and  water  flows  freely 
also  through  the  valves.  A  very  noticeable  advantage  of  the 
double-acting  engine  is  the  practical  impossiblity  of  any  leakage 
of  gas  into  the  engine  room,  because  the  piston,  instead  of  being 
open  to  the  atmosphere,  as  in  most  types  of  single-acting  engine,  is 
operated  from  a  piston  rod  running  through  a  metallic  stuffing- 
box.  The  operation  of  the  valve  shaft  is  obtained,  as  in  a  large 
steam  engine,  by  using  a  small  air  cylinder;  this  is  also  used  for 
turning  the  engine  over. 

"The  bore  and  stroke  of  the  Standard's  engine  are  each  10 
inches;  the  weight  is  7500  pounds,  or  25  pounds  per  horse-power; 
the  length  over  cylinders  is  8  feet  3  inches;  length  over  all,  10  feet 
4  inches;  the  total  height  is  5  feet  6^  inches,  of  which  4  feet  9J 
inches  come  above  the  center  of  the  shaft;  the  width  of  the  base 
is  30  inches;  while  the  greatest  width  over  cylinders  is  34  inches. 

"The  illustrations  of  the  new  motor,  as  shown,  serve  to  confirm 
the  impression  of  a  torpedo  boat  engine,  as  the  same  type  of 
supports,  connecting  rods,  cross-heads,  and  guides  are  here  used 
that  one  is  accustomed  to  in  the  other  kind  of  engine.  The 
double-acting .  principle  necessitates  some  radical  changes  from 
the  usual  marine  gasoline  motor  design,  such  as  water-cooling  the 
pistons,  connecting  rods,  valves  and  other  parts  exposed  to 
the  intense  heat  produced  in  cylinders  of  such  large  volume. 
Inlet  and  exhaust  valves  are  located  on  the  opposite  sides  of  the 
head,  as  is  customary  with  many  automobile  and  marine  engine 
builders.  The  upper  and  lower  ends  of  the  cylinders  are  alike, 
with  a  regular  marine  engine  piston  and  connecting  rod. 

"The  method  of  getting  the  gas  into  the  cylinders  is  very 
neatly  and  simply  worked  out,  as  is  shown  in  the  inlet  side.  One 
branch  pipe  leads  up  to  the  cylinders  from  the  center,  and  then 
runs  to  each  end  of  three  cylinders.  The  spark  and  throttle 
control  levers  are  mounted  on  top  of  the  air  cylinder,  which  con- 
trols the  travel  of  the  cam  shaft.  One  essential  point  of  difference 
between  the  ordinary  motor  and  this  motor  is  that  the  valves 
are  pulled  up  instead  of  being  pushed  up,  that  they  are 


MODERN  TYPES  OF  COMBUSTION  ENGINES        371 

balanced  and  that  they  are  water-cooled  by  a  stream  of  water  which 
flows  through  them  constantly.  This  type  of  valve  has  been 
adopted  by  the  Standard  Company  for  all  their  large  type  of  motors, 
and  has  been  found  to  work  exceedingly  well.  On  this  side,  also, 
are  located  the  trips  which  operate  the  sparkers  for  all  cylinders. 

"The  exhaust  valves  are  operated  from  a  cam  shaft  which  is 
a  duplicate  of  that  upon  the  inlet  side.  These  valves  are  also 
water-cooled  and  discharge  directly  into  a  large  water-cooled 
exhaust  box,  from  which  the  gases  are  led  to  the  muffler.  The 
oil  feeds  are  directly  under  the  exhaust  box,  with  individual  leads 
to  distribute  the  oil  to  the  different  bearings.  Directly  below 
and  behind  this  are  shown  the  air  inlets  to  the  cylinders  for  start- 
ing. In  a  large  motor  of  this  kind  the  problem  of  properly  cooling 
it  and  keeping  it  well  oiled  is  a  difficult  one,  and  the  working  out 
of  the  systems  by  which  these  results  are  accomplished  is  more 
complicated  than  it  would  be  for  a  small  motor,  but  the  owner 
of  a  motor  of  this  size  could  hardly  expect  to  operate  his  own 
engine,  and  in  reality  the  successful  working  of  the  motor  does  not 
demand  a  higher  order  of  skill  than  is  to  be  expected  from  the 
engineer  of  an  ordinary  triple-expansion  steam  engine.  While 
the  appearance  of  the  motor  is  complicated,  this  complication  is 
more  apparent  than  real.  Every  function  of  the  motor  has  been 
carefully  thought  out  and  provision  made  to  assure  its  proper 
working  under  all  conditions.  All  Standard  motors  of  large 
power  have  been  made  self-starting  and  reversing,  the  same  prin- 
ciples which  have  been  found  so  successful  being  employed  in 
this  latest  type:  but  in  the  double-acting  type  both  the  inlet  and 
exhaust  valves  are  mechanically  operated,  as  against  the  exhaust 
valves  only  in  the  other  self-starting  and  reversing  motors. 
Another  important  difference  is  that  in  this  type  all  the  cylinders 
are  cast  separately,  and  the  motor  is  really  two  three-cylinder 
motors  coupled  together  for  purposes  of  economy  in  construction 
and  replacement,  should  such  be  necessary. 

"The  self -starting  is  accomplished  by  compressed  air  being 
admitted  on  one  end  of  three  cylinders  by  a  special  set  of  cams. 
The  cylinders  turn  the  motor  until  it  takes  up  its  cycle  upon  gaso- 
line. The  cam  shafts  which  actuate  all  valves  are  so  made  as  to 
move  longitudinally  on  their  axes,  and  to  bring  appropriate  cams 
into  action  for  either  direction.  As  the  physical  labor  required  to 


372  INTERNAL  COMBUSTION  ENGINES 

perform  this  operation  would  be  considerable  in  a  motor  of  this 
size,  an  air  cylinder  is  added  to  perform  this  work,  so  that  the 
only  manual  labor  in  connection  with  running  the  motor  is 
that  in  operating  the  two  handles  shown  on  the  left  side  of 
Fig.  12-110.  One  lever  controls  the  position  of  the  cams, 
whether  for  ahead  or  astern,  while  the  other  controls  the  spark 
and  throttle.  In  this  motor  the  necessity  of  a  fly-wheel  is  entirely 
done  away  with,  and  operating  at  any  speed,  from  maximum 
to  minimum,  little  or  no  vibration  is  felt.  The  motor  is  mounted 
upon  a  base  of  angle  iron  with  castings  for  each  individual  bear- 
ing, and  has  the  usual  marine  collar  thrust  bearing." 


FIG.  12-111.  —  Engine  of  1907  Franklin  Car. 

The  Automobile  Gasoline  Engine.  —  It  would  be  beyond  the 
scope  of  this  book  to  enter  into  any  extensive  notice  of  automobile 
engines.  For  that  reason  only  a  few  illustrations  are  given  to 
show  the  various  methods  of  placing  the  valves  and  operating 
them,  the  methods  of  cooling  the  cylinder,  cylinder  and  frame 
construction,  etc.  In  general  the  four-cycle  engine  monopolizes 
the  automobile  field,  there  being  but  one  or  two  makers  who  use 
two-cycle  engines.  For  light  cars  the  horizontal  opposed  two- 
cylinder  type  of  engine  is  often  employed,  but  the  heavier  cars, 
universally  use  four-  or  six-cylinder  vertical  engines.  Regarding 
the  position  of  the  valves,  some  makers  place  both  inlet  and 
exhaust  valves  in  the  head.  This  type  is  best  exemplified  by  the 
Franklin  Engine  of  1907,  Fig.  12-111.  This  construction  is  of 
advantage  because  it  does  away  with  all  pockets  in  the  combus- 


MODERN   TYPES  OF  COMBUSTION  ENGINES         373 


tion   chamber.     In   this   engine   both   valves    are    mechanically 
operated.     Some  makers  use  the  automatic  type  of  inlet  valve, 


FIG.  12-112.  —  Continental  Automobile  Engine. 

which  in  such  cases  nearly  always  opens  downward.  This  valve, 
while  it  permits  of  simpler  engine  construction  than  the  mechani- 
cally operated  valve,  does 
not  give  as  good  service, 
and  for  that  reason  is  not 
as  frequently  used  as  for- 
merly. In  the  Continental 
Engine,*  Fig.  12-112,  both 
valves  are  placed  at  one 
side  of  the  cylinder  and 
both  are  mechanically  op- 
erated, opening  upward. 
In  the  18  horse-power 
Horch  engine,  Fig.  12-113  f 
the  inlet  valve  is  placed  in 
the  head,  the  exhaust  valve 
at  the  side.  The  35  horse- 
power  engine  of  the  same  FlQ  12_n3  _  lg  H  p  Horch  Automobile 
maker,  Fig.  12-114 J  has  Engine. 

*  The  Cycle  and  Automobile  Trade  Journal,  Oct.  1,  1907. 

t  Gasmotorentechnik,  April,  1906.        J  Gasmotorentechnik,  April,  1906. 


374 


INTERNAL  COMBUSTION  ENGINES 


both  valves  placed  at  one  side,  but  the 


FIG.  12-114.  —  35  H.P.  Horch  Automobile 
Engine. 

of  combustion  chamber.  The  outside, 
valve.  The  large  inlet  area 
improves  the  volumetric  effi- 
ciency. This,  however,  is  in 
large  part  also  made  possible 
by  the  fact  that  the  greater 
part  of  the  hot  burned  gases 
escapes  through  the  auxiliary 
exhaust  valve  which  opens 
when  the  piston  is  near  the 
lower  dead  center.  The  re- 
mainder of  the  gases  passing 
out  through  the  inner  valve 
at  the  top  during  the  up 
stroke  of  the  piston  does  not 
tend  to  heat  the  valve  very 
much. 

Of  the  automobile  engines 


inlet  valve  over  the  ex- 
haust valve.  Both  are 
mechanically  operated. 
The  Moore  engine,  Fig. 
12-115,*  shows  the  valves 
upon  opposite  sides,  both 
mechanically  operated. 
The  1908  model  of  the 
Franklin  engine  finally,,, 
shows  a  type  of  valve 
gear  different  from  any  of 
those  so  far  described  in 
that  the  main  exhaust 
and  the  inlet  valves  are 
combined  in  one  concen- 
tric valve  placed  in  the 
head.  This,  as  may  be 
seen  from  Fig.  12-116, 
results  in  an  ideal  form 
larger,  valve  is  the  inlet 


FIG.  12-115.  —  Moore  Automobile 
Engine. 


Cycle  and  Automobile  Trade  Journal,  April,  1906. 


MODERN  TYPES  OF  COMBUSTION  ENGINES        375 

illustrated,  the  Franklin  engine  shows  the  construction  employed 
for  air-cooled  cylinders;  all  of  the  other  engines  are  water-cooled. 
4.  OIL  ENGINES.  — The  term  "oil  engines"  usually  refers  to 
engines  using  kerosene,  crude  oil,  or  any  one  of  the  so-called  dis- 
tillates. All  of  these  fuels  are  more  difficult  to  vaporize  than 
gasoline  and  the  formation  of  the  proper  fuel  mixture  is  therefore 
generally  a  less  simple  process.  Some  of  the  types  use  a  special 
vaporizer,  in  others  the  fuel  is  sprayed  directly  into  the  combus- 
tion chamber  or  into  an  extension  of  it. 


FIG.  12-116.  —  1908  Model,  Franklin  Engine. 

Liquid  fuel  engines  in  general  labor  under  the  disadvantage 
as  compared  with  gas  engines  in  that  the  limit  of  power  in  a  single 
cylinder  is  reached  much  earlier.  The  reason  for  this  is  that  as 
the  cylinder  volume  grows,  the  difficulties  of  forming  and  main- 
taining a  uniform  fuel  mixture  increase  very 'rapidly,  and  the 
difficulties  of  proper  ignition  increase  correspondingly.  The 
result  is,  at  least  as  far  as  present  practice  is  concerned,  that 
while  the  economic  limit  in  one  single-acting  cylinder  using  gas 
is  in  the  neighborhood  of  perhaps  400  horse-power,  the  limit  in 
single-cylinder  single  acting  oil  engines  is  not  over  200  horse-power. 
Hence  the  subdivision  of  the  power  required  among  several 
cylinders  commences  much  sooner  in  oil  than  in  gas  engines. 

The  most  important  point  of  distinction  among  the  various 


376  INTERNAL  COMBUSTION  ENGINES 

oil  engines  is  probably  the  way  in  which  the  combustible  mixture 
is  formed.  We  distinguish  the  following  methods: 

(a)  The  fuel  is  forced  directly  into  the  combustion  chamber 
at  the  end  of  or  during  the  compression  stroke.  Usually  a  spray- 
ing nozzle  is  employed. 

(6)  The  fuel  is  mechanically  atomized  and  sprayed  into  the 
current  of  air  on  the  suction  stroke. 

(c)  The  fuel  is  sprayed  into  a  vaporizing  chamber  connected 
to  the  cylinder  without  interposition  of  a  valve. 

(d)  The  fuel  is  vaporized  by  the  agency  of  heat  in  a  separate 
vaporizer.     The  air  passing  through  the  vaporizer  forms  the  fuel 
mixture  and  this  enters  the  engine  already  prepared. 

The  following  descriptions  of  various  oil  engines  will  illustrate 
the  various  methods  outlined: 

Among  the  most  important  oil  engines  found  on  the  American 
market  are  the  following:  The  Hornsby-Akroyd  kerosene  engine, 
ii  machine  of  English  origin  made  by  the  De  La  Vergne  Machine 
Company,  of  New  York;  the  De  La  Vergne  two-cycle  oil  engine, 
brought  out  by  the  same  company  within  the  last  month  or  two; 
the  Mietz  &  Weiss  oil  engine  made  by  the  A.  Mietz  Iron  Foundry 
&  Machine  Works  of  New  York;  and  the  American  Diesel  engine 
manufactured  by  the  American  Diesel  Engine  Company.  It 
should  be  stated  that  many  of  the  engines  described  under  the 
head  of  small  and  medium  sized  gas  engines  can  be  run  on  oil  by 
using  suitable  vaporizers.  Thus  the  Fairbanks-Morse  Company 
and  several  other  makers  furnish  vaporizing  attachments  by 
means  of  which  their  engines  may  be  successfully  run  on  kero- 
sene, crude  oil,  or  distillate. 

The  Hornsby-Akroyd  Oil  Engine.  —  Figs.  12-117  and  12-118 
show  a  longitudinal  and  a  transverse  section  respectively  of  this 
important  oil  engine,  while  Fig.  12-119  shows  the  general  appear- 
ance of  a  single-cylinder  engine.*  The  Hornsby  engines  built  in 
this  country  are  all  horizontal  machines  of  the'  four-cycle  type. 
The  exhaust  and  inlet  valves  are  of  the  poppet  type  and  located 
in  a  valve  box  at  the  side  of  the  cylinder,  Fig.  12-118.  They 
open  upward  and  are  operated  by  levers  passing  under  the  cylin- 
der by  means  of  cams  on  the  half-time  shaft.  The  exhaust  cam 
is  so  designed  that  on  starting  the  compression  can  be  relieved 
*  Catalogue  of  the  De  La  Vergne  Machine  Co. 


MODERN   TYPES  OF  COMBUSTION  ENGINES         377 


378 


INTERNAL  COMBUSTION  ENGINES 


by  shifting  the  cam  on  the  shaft.  The  supply  of  oil  is  taken  from 
a  tank  in  the  base»of  the  machine  by  a  pump  operated  from  the 
lay  shaft,  and  forced  into  the  vaporizer  chamber  A,  through  a 
spray  nozzle.  The  governor  is  of  the  fly-ball  type  and  controls 
the  speed  by  dividing  the  constant  quantity  of  oil  furnished  by 
the  pump  into  two  parts,  one  of  which,  in  proportion  to  the  load, 
enters  the  nozzle,  the  other  part  flows  back  to  the  tank.  The 
nozzle  and  overflow  valve  are  shown  in  greater  detail  in  Chapter 
VIII. 


FIG.  12-118.  —  Transverse  Section  Hornsby- 
Akroyd  Oil  Engine. 

The  vaporizer  chamber  is  furnished  with  internal  webs  to 
increase  the  vaporizing  surface,  and  is  protected  against  radiation 
on  the  outside  by  a  hood. 

To  start  the  engine  the  vaporizer  is  first  heated  by  a  lamp 
which  constitutes  a  part  of  the  equipment.  After  the  chamber 


MODERN  TYPES  OF  COMBUSTION  ENGINES        379 

is  hot  enough,  a  few  quick  strokes  of  the  pump  by  means  of  the 
hand  lever,  Fig.  12-118,  while  the  engine  is  being  turned  over  in 
the  normal  direction,  usually  suffices  to  start  it.  After  starting,  the 
heat  of  combustion  is  enough  to  keep  the  vaporizer  at  a  dull  red 
heat  and  to  explode  the  charges  regularly,  so  that  no  special 
igniter  is  required. 


FIG.  12-119.  — Single  Cylinder  Hornsby-Akroyd  Oil  Engine. 

The  method  of  operation  may  be  explained  as  follows:  On  the 
suction  stroke  of  the  piston  the  pump  injects  oil  into  the  vaporizer. 
This  is  almost  instantly  vaporized,  but  as  yet  the  mixture  is  not 
explosive  because  the  vapor  is  mixed  mainly  with  burned  gases 
which  remain  from  the  previous  explosion.  On  the  return  stroke, 
the  piston  compresses  the  air  and  forces  a  part  of  it  into  the 
vaporizer.  It  is  possible  that  some  time  during  the  compression 
stroke  the  vapor  may  commence  to  burn  in  the  vaporizer,  but  the 
flame  does  not  stride  out  because  the  velocity  of  air  flowing  in 
through  the  narrow  neck  of  the  vaporizer  is  greater  than  the 
velocity  of  flame  propagation.  Near  the  end  of  the  compression 
stroke  the  reverse  takes  place,  the  flame  strikes  out  with  explo- 
sive force  and  drives  the  piston  forward  on  the  expansion  stroke. 
This  is  followed  by  the  exhaust  stroke,  after  which  the  operation 
is  repeated. 


380 


INTERNAL  COMBUSTION  ENGINES 


These  engines. have  given  very  satisfactory  service  and  many 
of  them  are  in  use  for  a  variety  of  purposes.  They  are  made  in 
sizes  from  2^  to  125  horse-power,  those  above  32  horse-power 
being  of  the  two-cylinder  type  illustrated  in  Fig.  12-120.  This 
design  has  lately  been  modified  in  that  the  two  overhanging  fly- 
wheels have  been  replaced  by  a  single  wheel  placed  next  to  the  belt 
pulley  between  the  two  cylinders. 


FIG.  12-120.  —  Twin  Cylinder  Hornsby-Akroyd  Oil  Engine. 

The  De  La  Vergne  Two-cycle  Oil  Engine.  —  This  is  a  vertical 
machine  recently  brought  out  by  the  De  La  Vergne  Machine 
Company  and  described  in  Power,  November,  1907,  to  which  the 
following  illustrations  are  due: 

Figure  12-121  shows  that  the  cylinder  is  of  the  ordinary  two- 
cycle  construction,  the  piston  controlling  the  inlet  and  exhaust 
ports.  The  vaporizer  chamber  V  is  formed  by  an  extension  of 
the  cylinder,  but,  in  contradistinction  to  the  Hornsby  engine,  no 
contracted  neck  is  used  opening  into  the  vaporizer.  On  the  down 
stroke  of  the  piston  the  air  compressed  in  the  crank  case  rushes 
into  the  cylinder  as  soon  as  the  inlet  port  is  uncovered.  On  the 
up  stroke  only  air  is  compressed,  the  oil  not  being  injected  by  the 


MODERN  TYPES  OF  COMBUSTION  ENGINES        381 

pump  through  the  nozzle  N  until  near  the  upper  dead  center. 
The  oil  instantly  vaporizes  and  burns,  ignition  being  produced 
by  the  hot  vaporizer  walls.  Of  course  the  vaporizer  must  be 


FIG.  12-121.  —  De  La  Vergne  Two-cycle  Oil  Engine. 

externally  heated  to  start  the  engine.  The  method  of  operation 
outlined  has  the  advantage  that  since  only  air  is  compressed  no 
pre-ignition  can  take  place. 

The  details  of  the  spray  nozzle  N  are  shown  in  Fig.  12-122. 


FIG.  12-122.  —  Spray  Nozzle  De  La  Vergne  Two-cycle  Oil 
Engine. 

They  are  so  simple  as  to  hardly  require  explanation.  The  ball 
check  shown  serves  to  protect  the  oil  pipe  against  the  force  of 
the  explosions. 


382 


INTERNAL  COMBUSTION  ENGINES 


The  engine  is  governed  by  suiting  the  quantity  of  oil  to  the 
load.  This  is  done  by  putting  the  pump  plunger  under  control 
of  the  governor  in  the  fly-wheel.  Power  gives  the  following 
description  of  this  device  (see  Fig.  12-123): 


& 


"The  frame  J?*1  is  fastened  with  two  studs  concentrically  to  the 
inside  of  the  fly-wheel,  and  to  the  frame  is  pivoted  a  cam  ring  R 
which  has  on  the  fly-wheel  side  a  projection  B,  and  back  of  that 


MODERN  TYPES  OF  COMBUSTION  ENGINES        383 

the  cam  projection  C,  which  lifts  the  roller  A  once  each  revolution 
of  the  fly-wheel,  thereby  actuating  the  oil-pump  plunger  P. 
The  length  of  stroke  imparted  to  the  plunger  is  determined  by 
the  lever  L,  pivoted  to  the  frame.  A  wedge  W  on  the  lever  L 
separates  the  cam  ring  from  the  frame  F.  When  the  engine  is 
started  the  governor  does  not  come  into  action  until  normal  speed 
is  approached.  A  decrease  in  load  will  cause  the  speed  to  increase, 
when  the  centrifugal  force  of  the  counterweight  K  will  overcome 
the  tension  of  the  spring  S,  moving  the  wreight  outward  and 
thereby  withdrawing  the  wedge  W.  The  spring  E  keeps  the 
roller  A  in  contact  with  the  cam  ring  R,  and  when  the  wedge  is 
withdrawn  the  buffer  G  cannot  actuate  the  pump  plunger.  The 
knob  H  is  used  for  injecting  oil  at  the  start,  and  the  lock  nuts  N 
serve  for  limiting  the  stroke  of  the  pump.  The  two  concentric 
slots  in  the  frame  F  allow  for  adjustment  when  it  is  desired  to 
greatly  change  the  normal  speed  of  the  engine.  For  smaller  speed 
variations  the  spring  S  and  the  weight  K  can  be  shifted  in  the 
holes  of  the  lever  L." 

At  present  two  sizes  of  this  engine  are  made.  That  illustrated 
is  of  15  horse-power,  the  single  cylinder  type  gives  7^  horse-power. 
In  each  case  the  cylinders  are  7  inches  by  7.5  inches,  the  normal 
speed  being  450  r.p.m. 

The  Mietz  &  Weiss  Oil  Engine.  —  This  is  a  very  successful 
engine  which  has  been  on  the  market  for  some  years.  While  it 
operates  on  the  ordinary  three-port  two-cycle  principle,  it  em- 
bodies some  unusual  features.  Fig.  12-124  shows  the  horizontal 
type  in  cross-section,  and  Fig.  12-125  its  general  appearance  in 
elevation.  From  Fig.  12-124  the  operation  of  the  engine  must 
be  clear  without  much  further  explanation. 

The  fuel  pump  P  takes  the  oil  from  a  tank  mounted  on  the 
crank  case  and  injects  it  into  the  cylinder  just  after  the  piston 
has  covered  the  exhaust  port  E.  The  oil  falls  on  the  projection 
V  and  is  instantly  vaporized  by  heat  from  the  hot  bulb  I,  and 
from  the  cylinder  head,  which,  as  will  be  noted,  is  not  water- 
jacketed.  Ignition  is  produced  by  means  of  the  bulb  7,  which 
acts  very  much  like  the  ordinary  hot  tube.  A  kerosene  or  oil 
lamp,  shown  in  position,  serves  to  heat  the  bulb  before  starting. 
Five  minutes  is  usually  sufficient  for  this  operation. 

The  unusual  feature  of  this  engine  consists  in  the  cooling 


384 


INTERNAL   COMBUSTION  ENGINES 


water  arrangements.  Instead  of  circulating  the  water,  as  is 
ordinarily  done,  it  is  allowed  to  evaporate  in  the  jacket,  being 
kept  at  a  constant  level  by  a  float  valve.  The  vapor  formed  col- 
lects in  the  dome  S,  Fig.  12-124,  and  is  by  means  of  the  bent  pipe 
shown  led  to  the  intake  port  of  the  cylinder  where  it  mixes  with 
the  air.  There  are  several  excellent  reasons  for  this  arrangement 
in  oil  engines.  The  water  vapor  helps  to  form  a  mixture  of  high 
specific  heat,  thus  reducing  the  danger  of  pre-ignition  and  allow- 


FIG.  12-124.  —  Details  of  Mietz  &  Weiss  Two-cycle  Oil  Engine. 

ing  of  higher  compression  pressures.  The  principle,  however,  is 
not  new,  since  Banki  and  perhaps  several  others  before  him  have 
used  it.  It  is  also  claimed  that  the  vapor  assists  in  the  preven- 
tion of  carbon  deposits.  The  method  further  has  the  general 
advantage  that  but  little  jacket  water  is  used  compared  with  the 
ordinary  method  of  operation. 

The  method  of  governing  this  engine  is  not  clearly  shown, 
but  it  consists  in  adjusting  the  stroke  of  the  fuel  pump  to  suit 
the  load  by  means  of  a  shifting  eccentric  on  the  main  shaft. 

The  stationary  Mietz  &  Weiss  engine  is  built  in  single-cylinder 


MODERN  TYPES  OF  COMBUSTION  ENGINES        385 


units  from  1  to  30  horse-power,  while  the  40  and  60  horse-power 
sizes  are  twin  engines. 


bL 
I 

o 

.2 
o 

>> 

o 

6 


This  firm  also  builds  vertical  marine  engines,  the  operation 
of  which  is  the  same  as  that  of  the  horizontal  machine  except  that 
the  water  injection  scheme  is  not  used. 

The  Diesel  Engine.  —  The  Diesel  engine  is  to-day  built  by  a 
number  of  firms  in  Europe  and  by  the  American  Diesel  Engine 


386 


INTERNAL  COMBUSTION  ENGINES 


Company  in  this  country.  In  all  cases,  the  various  constructions 
are  of  the  vertical  four-cycle  type,  but  European  builders  favor 
the  open  ^1-frame,  while  the  American  makers  have  adopted  the 
enclosed  box  frame. 

Figure  12-126  gives  a  general  idea  of   the  appearance  of   the 
American  Diesel  engine,  while  Fig.  12-127  shows  the  construction. 


FIG.  12-126.  —  American  Diesel  Engine. 

The  massive  self-contained  build  of  this  machine,  necessitated  of 
course  by  the  high  pressures  occurring  in  its  cycle  of  operation, 
is  very  noticeable.  The  method  of  operation  of  this  machine  has 
already  been  explained  in  Chapter  XI,  to  which  the  reader  is 
referred. 

The  valve  construction  of  this  engine  is  very  simple,  as  shown 
in  Fig.  12-128.     The  exhaust  valve  opens  upward,  the  inlet  valve 


MODERN  TYPES  OF  COMBUSTION  ENGINES  '      387 


downward;  both  are  located  in  a  small  chamber  at  the  side  of  the 
cylinder.  The  fuel  injection  valve  /  is  opened  by  the  bell-crank 
B,  which  is  operated  by  a  cam  on  the  lay  shaft,  and  closed  by 
a  helical  spring  S.  Surrounding  the  spindle  of  the  injection  valve 


FIG.  12-127.  —  Cross-section  American  Diesel  Engine. 

are  placed  the  atomizing  arrangements  by  which  the  oil  is  very 
finely  divided  through  the  agency  of  highly  compressed  air,  as 
soon  as  B  opens  the  valve.  The  stroke  of  the  lever  B  is  uniform, 
hence  the  injection  valve  always  opens  to  the  same  amount  and 
for  the  same  length  of  time,  whatever  the  load  on  the  engine. 
To  govern  the  speed,  the"  governor  controls  the  stroke  of  the 


388 


INTERNAL  COMBUSTION  ENGINES 


pump  which  furnishes  the  oil  to  the  valve.  The  lower  the  load  on 
the  engine,  the  later  in  the  stroke  of  the  oil  pump  does  the  deliv- 
ery of  oil  to  the  injection  valve  commence.  One  method  of  doing 
this  is  explained  in  Chapter  XIV,  under  Details  of  Governors. 


FIG.  12-128.  —  Valve  Construction,  American  Diesel 
Engine. 

The  American  Diesel  engine  is  built  in  sizes  from  75  to  450 
B.  H.  P.,  mostly  in  three-cylinder  units. 

The  Priestman  Oil  Engine.  —  This  English  machine,  Fig. 
12-129,*  is  mentioned  here  because  the  means  used  for  forming 
the  combustible  mixture  are  different  from  those  so  far  described. 
The  engine  is  of  the  horizontal  single-acting  type,  The  exhaust 
valve  is  mechanically  operated  by  an  eccentric  on  the  shaft.  The 
same  eccentric  rod  also  operates  a  small  air  pump  e  which  keeps 
up  an  air  pressure  of  from  30  to  40  pounds  on  top  of  the  oil  in  the 

*Guldner,  p.  118. 


MODERN   TYPES  OF  COMBUSTION  ENGINES        389 

supply  tank  b.  The  inlet  valve  c  is  automatic.  On  the  suction 
stroke  the  piston  draws  a  charge  of  finely  divided  oil,  mixed  with 
air  furnished  by  the  spray  maker,  into  the  vaporizer  tt,  together 
with  a  large  quantity  of  auxiliary  air  to  form  the  proper  combus- 
tible mixture.  The  vaporizer,  heated  at  the  start  by  external 
means,  is  during  operation  kept  by  the  exhaust  gases  at  sufficient 
heat  to  completely  vaporize  the  oil  before  it  passes  out  on  its  way 
to  the  inlet  valve.  Thus  the  mixture  reaches  the  cylinder  com- 
pletely prepared.  The  spray  maker  and  vaporizer  are  explained 
in  greater  detail  in  Chapter  VIII. 


FIG.  12-129.  —  Priestman  Oil  Engine. 

The  cylinder  operates  on  the  ordinary  four-cycle  principle; 
ignition  is  by  electric  spark.  In  the  later  Priestman  engines  a 
small  amount  of  water  from  the  jacket  is  admitted  to  the  cylinder 
each  cycle,  after  the  principle  of  Banki. 

The  Fairbanks- Morse  Crude  Oil  Vaporizer.  —  In  the  fourth 
type  of  vaporizer  the  oil  is  not  preliminarily  sprayed  or  atomized, 
as  is  done  in  the  Priestman  vaporizer,  but  simply  vaporized  by 
the  heat  of  the  exhaust  gases.  The  piston  then  generally  draws 
a  part  of  the  necessary  air  through  the  vaporizer  and  saturates 
this  with  the  oil  vapor.  The  rest  is  added  to  form  the  proper 
mixture  just  before  the  inlet  valve.  Of  this  type  is  the  "  Econo- 
mist" retort,  already  described  in  Chapter  VIII.  Another  type 
is  that  made  by  the  Fairbanks-Morse  Company,  and  illustrated 


390 


INTERNAL  COMBUSTION  ENGINES 


in  Fig.  12-130.  G  is  the  main  vaporizer  chamber.  The  oil  pump 
furnishes  oil  through  the  pipe  F  to  the  reservoir  R  on  top  of  the 
chamber.  The  regulating  valve  T  returns  the  excess  pumped 
to  the  main  supply  through  the  pipe  0.  From  R  the  oil  is  allowed 
to  trickle  slowly  downward  over  surfaces  heated  by  the  exhaust 
gases.  These  come  in  through  the  pipe  N,  but  the  volume  enter- 
ing G  is  controlled  by  the  position  of  the  valve  E,  which  sends  a 
part  into  G,  the  rest  directly  out  through  X,  depending  upon  the 
demands  of  the  vaporizer.  Air  enters  the  chamber  through  C. 


FIG.  12-130.  —  Fairbanks-Morse  Engine 
with  Crude  Oil  Vaporizer. 

On  its  way  upward  it  saturates  itself  with  oil  vapor  and  finally 
flows  out  through  B  to  the  engine.  The  auxiliary  air  supply  is 
furnished  through  A. 

Any  vaporizer  of  this  type  labors  under  the  disadvantage, 
already  mentioned  in  the  case  of  the  "Economist"  retort,  that 
not  all  of  the  oil  can  be  utilized.  As  the  vaporization  proceeds, 
the  oil  gets  heavier,  the  amount  of  vapor  evolved  grows  less  at 
the  temperature  maintained,  and  the  useless  residue  must  finally 
be  drawn  off.  In  the  apparatus  above  described  provision  for 
this  has  been  made  through  the  drain  cock  D.  W  is  a  heating 
lamp  to  heat  the  vaporizer  on  starting. 

5.  THE  ALCOHOL  ENGINE.  —  The  points  of  difference  between 
the  alcohol  engine  and  any  other  gas  engine  have  already  been 


MODERN  TYPES  OF  COMBUSTION  ENGINES        391 

mentioned  in  Chapter  VIII.  In  constructive  details  these  engines 
do  not  differ  from  the  rest  except  that  the  compression  is  carried 
higher  than  in  other  liquid  fuel  engines.  The  main  feature  dis- 
tinguishing them  is  in  the  arrangements  for  forming  the  com- 
bustible mixture,  and  the  various  expedients  adopted  have  been 
thoroughly  discussed  under  the  head  of  vaporizers  in  the  chapter 
mentioned.  Recent  experiments  have  disproven  the  old  state- 
ment that  an  alcohol  engine  cannot  be  started  from  the  cold. 
Much  depends  upon  the  position  of  the  carbureter  with  reference 
to  the  inlet  valve  ports,  and  after  paying  due  attention  to  this 
point,  a  gasoline  automobile  engine  has  been  successfully  operated 
on  alcohol  without  change.  This  bears  out  the  experience  of  the 
Deutz  Company  in  whose  alcohol  engines  only  a  spray  nozzle 
placed  very  close  to  the  inlet  valve  is  used.  An  ordinary  gasoline 
carbureter  can  be  made  to  act  in  somewhat  the  same  way.  Ameri- 
can practice  regarding  alcohol  engines  is  for  obvious  reasons 
somewhat  behind  that  of  Europe,  but  the  indications  are  at  present 
that  this  condition  will  not  long  exist. 


CHAPTER  XIII 


GAS    ENGINE    AUXILIARIES:     IGNITION,     MUFFLERS,     AND     STARTING 

APPARATUS 

Ignition.  —  There   are    four    methods    of    igniting    the    com- 
bustible charge  in  a  gas  engine.     Some  of  these  are  still  in  use. 
others  belong  to  the  period  of  gas-engine 
development.     These    methods   are   the 
following : 

1.  Ignition  by  an  open  flame. 

2.  Ignition  by  hot  tube. 

3.  Ignition  by  heat  of  compression,  and 

4.  Ignition  by  electric  spark. 
Ignition  by  open  flame  is  practically 

obsolete,  and  ignition  by  hot  tube  is  also 
fast  falling  into  disuse.  As  a  matter  of 
fact,  except  for  the  Diesel  engine,  the 
Hornsby-Akroyd  and  a  few  others,  which 
ignite  the  charge  or  fuel  by  heat  of  com- 

Explosion  .  -  ,         .          *      •         •,  • 

Port  pression,  the  method  of  igniting  the 
charge  by  the  electric  spark  is  to-day 
the  means  most  generally  employed. 

i.  Ignition  by  Open  Flame.  —  This 
method  has  been  superseded  probably 
because  of  its  occasional  failure  and  the  obvious  danger  con- 
nected with  its  use  under  certain  conditions. 

The  simplest  arrangement  of  this  type  is  Barnett's  ignition 
cock,  Fig.  13-1.*  This  consists  of  a  hollow  plug  which  works  in 
a  shell  having  two  ports,  1  and  2.  The  former  opens  to  the 
atmosphere  and  communicates  with  an  outside  flame,  A,  the 
latter  opens  into  the  cylinder.  The  port  3  in  the  plug  is  of  such 
a  size  that  it  may  communicate  either  with  port  1  or  2.  but  never 

*  Clerk,  The  Gas  and  Oil  Engine,  p.  207. 
392 


FIG.  13-1.  —  Barnett's 
Ignition  Cock. 


GAS  ENGINE  AUXILIARIES 


393 


with  both  at  the  same  time.  Inside  the  plug  is  placed  a  gas  jet 
as  shown.  Gas  should  be  admitted  to  this  at  such  a  rate  that 
the  flame  burns  inside  of  the  plug  and  not  out  through  the  ports 
3  and  1.  The  proper  size  of  the  ports  has  much  to  do  with  the 
proper  admission  of  air  to  the  inside  of  the  plug  to  keep  the 
flame  alive,  as  shown  by  the  arrows.  If  now  the  plug  is  quickly 
turned  through  90  degrees,  making  the  port  3  register  with  port  2, 
enough  air  is  contained  in  the  plug  to  keep  the  flame  burning 
during  the  interval,  and  the  combustible  mixture,  entering  the 
plug  much  as  the  air  enters  it  in  the  first  position,  is  instantly 
ignited.  Here  again  the  proper  size  of  the  ports  is  of  importance, 
for  if  the  mixture  cannot  circulate  through  the  plug,  it  must  reach 
the  flame  by  diffusion.  The  chances  are  that  in  that  time  the 
flame  has  died  out  and 
ignition  fails.  The  flame 
is  blown  out  by  the 
force  of  the  explosion, 
or  dies  out  for  lack  of 
air,  but  is  immediately 
relighted  by  the  out- 
side flame,  A,  when  the 
plug  returns  to  its  for- 
mer position. 

Barnett's  scheme 
was  open  to  the  objec- 
tion that  since  the  flame  chamber  in  the  plug  was  always  under 
atmospheric  pressure,  the  combustible  mixture,  if  compressed  to 
any  extent,  might  extinguish  the  flame  by  sudden  inrush  when 
communication  was  established.  Several  methods  to  obviate  this 
were  invented,  notably  by  Otto  and  by  Clerk.  The  latter  differs 
from  the  former  in  that  it  will  operate  at  higher  engine  speeds; 
Otto's  scheme  failing  at  comparatively  low  speeds.  A  very  simple 
solution  of  the  problem  is  shown  in  Koerting's  igniter,  Fig.  13-2.* 
The  plug,  b,  see  left-hand  section,  is  practically  a  divergent  nozzle. 
The  pressure  of  the  combustible  mixture  during  compression  raises 
the  plug,  and  some  of  the  mixture,  escaping  through  the  fine  opening, 
c,  and  expanding  through  b,  is  ignited  by  the  open  flame,  d.  At  the 
instant  the  piston  reverses,  the  plug  is  forced  down  by  the  plunger, 
*  Schottler,  Die  Gasmaschine. 


FIG.  13-2. — Koerting  Igniter. 


394 


INTERNAL  COMBUSTION  ENGINES 


a,  closing  both  the  top  and  the  bottom  openings.  But  the  mix- 
ture contained  in  the  nozzle,  6,  keeps  on  burning  until,  at  the 
instant  the  side  openings,  e,  are  freed,  the  flame  strikes  into  the 
cylinder  and  ignites  the  charge.  The  right-hand  section,  Fig. 
13-2,  shows  the  ignition  position. 

2.  Ignition  by  Hot  Tube.  —  The  simplest  form  of  the  hot 
tube  ignition  apparatus  has  already  been  shown  in  Fig.  11-5 
Chapter  XL  It  consists  merely  of  a  small  tube  3  or  4  inches  long, 
of  steel,  porcelain,  or  platinum.  The  open  end  of  this  tube  is  in 
communication  with  the  combustion  chamber,  the  other  end  is 
closed.  The  tube  is  kept  red  hot  for  a  certain  part  of  its  length, 

generally  by  means  of  a  Bunsen 
burner.  A  chimney  surrounds 
both  burner  and  tube  to  prevent 
loss  of  heat  by  radiation  as  far 
as  possible. 

The  action  of  the  hot  tube 
may  be  explained  as  follows :  At 
the  end  of  the  exhaust  stroke 
the  tube  is  filled  with  burned 
gases,  and  these  are  not  replaced 
by  the  fresh  mixture  even  at 
the  end  of  the  next  suction 
stroke,  because  the  time  avail- 
able is  too  short  for  diffusion. 
•  During  the  compression  stroke 

the  burned  gases  are  being  compressed  into  the  closed  end  of  the 
tube  and  are  followed  up  by  the  fresh  mixture.  But  no  explosion 
follows  even  if  this  mixture  reaches  the  red-hot  part  of  the  tube 
as  long  as  the  velocity  of  flame  propagation  out  of  the  tube  is  less 
than  the  velocity  of  the  fresh  charge  into  the  tube.  When  the 
former  becomes  greater  than  the  latter,  which  happens  at  or  just, 
before  the  piston  reaches  the  dead  center,  the  flame  shoots  out  and 
ignites  the  charge.  It  is  plain,  however,  that  in  the  device  shown  in 
Fig.  1 1-5  the  position  of  the  hot  zone  along  the  tube  must  be  about 
right  or  pre-ignition  may  result.'  Want  of  adjustment  in  this 
arrangement  has  led  to  the  improved  hot  tube  shown  in  Fig.  13-3. 
In  this  case  the  position  of  the  hot  zone  along  the  tube  may  be 
varied  as  shown,  thus  giving  some  control  over  the  time  of  ignition. 


GAS  ENGINE  AUXILIARIES 


395 


In  order  to  completely  control  the  time  of  ignition  the  or- 
dinary hot  tube  has  been  perfected  by  the  addition  of  a  so-called 
timing  valve. 

In  Fig.  13-4,  G  is  the  tube  kept  hot  in  the  ordinary  way. 
Timing  valve  E  is  normally  kept  closed  by  the  coil  spring  C.  At 
the  proper  time  in  the  cycle  the  ignition 
cam  (not  shown),  through  the  link,  B, 
and  the  bell-crank,  A-D,  compresses 
the  spring,  C,  and  opens  the  valve. 
Ignition  then  ensues.  The  valve  is 
kept  open  during  the  expansion  and 
exhaust  strokes.  The  time  of  ignition 
may  be  changed  by  changing  the  posi- 
tion of  the  cam. 

Timing  valves  are  open  to  the  ob- 
jection that  they  are  very  difficult  to 
keep  in  shape  under  the  high  tempera- 
tures occurring.  To  avoid  the  use  of 
the  small  valve  in  the  cylinder,  Koert- 
ing  has  used  the  scheme  shown  in  Fig. 


Tube  with 
Timing  Valve. 


13-5;  a  is  an  open 
hot  tube  made  of  porcelain.  In  it  there  is 
placed  the  small  platinum  tube,  c.  Dur- 
ing compression  some  of  the  mixture  es- 
capes through  c  and  the  valve  k.  When 
ignition  is  desired,  k  shuts  the  exit  and  the 
flame  in  a  strikes  back  into  the  cylinder. 
Hot  tubes  may  be  from  two  to  four 
inches  long,  and  from  one-quarter  to  one- 
half  inches  internal  diameter.  They  may 
be  made  of  steel,  platinum,  or  Porcelain. 
Porcelain  is  best  because  cheap  and  nearly 
indestructible  by  heat. 

The  hot  tube  finds  application  in  small 
and  medium   sized   stationary  machines 
only.     It  is  fully  as  cheap  to  operate  as 
electric  ignition  and  just  as  certain. 
In  large  machines  this  method  of  ignition  is  not  as  satisfac- 
tory, because  the  ignition  itself  is  hardly  sharp  enough  for  the 
large  volume  of  gas,  and 'because  in  many  cases  the    distance 


FIG.  13-5.  —  KoertingHot 
Tube  Igniter. 


396  INTERNAL  COMBUSTION  ENGINES 

the  flame  has  to  strike  is  too  great.  Care  should  be  taken  to 
place  the  tube  at  the  proper  point,  i.e.,  where  a  good  mixture  at 
the  opening  of  the  tube  is  insured,  and  where  the  opening  cannot 
be  clogged  by  oil  or  water. 

3.  Igniting  the  Charge  by  Heat  of  Compression.  —  This 
method  of  igniting  the  charge  is  practically  limited  to  liquid 
fuels  and  is  carried  out  in  several  ways. 

(a)  Only  air  is  compressed  to  a  very  high  degree  so  that  its 
temperature  is  high  enough  to  ignite  the  fuel  as  it  is  injected  at 
the  beginning  of  the  working  stroke.     This  is  Diesel's  method. 

(b)  The  charge  may  be  ignited  by  means  of  a  hot  bulb  or 
chamber   connected   to   the   combustion   chamber   proper   by   a 
narrow  neck  or  opening.     There  are  two  modifications  of  this 
method.     In  the  one  the  fuel  is  injected  into  the  combustion 
chamber  on  the   suction   stroke.     During   the   next   stroke   the 
mixture  is  compressed  into  the  hot  bulb  and  ignites.     The  com- 
bustion, however,  is  confined  to  the  bulb  until,  near  the  end  of  the 
compression  stroke,  the   velocity  of  flame  propagation  exceeds 
the  velocity  of  gases  entering  the  narrow  neck  of  the  bulb,  when 
the  flame  strikes  out  and  general  ignition  ensues.     The  action 
of  the  bulb  is  therefore  very  similar  to  that  of  the  open  hot  tube. 
The  main  difference  is  that  after  the  bulb  has  been  externally 
heated  at  the  start,  the  heat  of  compression  soon  keeps  the  walls 
of  the  bulb  at  a  sufficiently  high  temperature  so  that  the  external 
flame  can  be  extinguished. 

In  the  second  modification,  the  hot  bulb  or  chamber  is  used 
at  the  same  time  as  a  vaporizer.  Thus  in  the  Hornsby-Akroyd 
engine,  the  fuel  is  injected  into  the  chamber  by  a  pump  at  the 
beginning  of  the  suction  stroke.  The  piston  draws  nothing  but 
air  on  this  stroke,  which  air  is  partly  forced  into  the  bulb  on  the 
return  stroke.  Here  it  mixes  with  the  oil  vapor,  which  formed, 
due  to  contact  with  the  hot  walls,  and  while  combustion  may 
ensue  it  cannot  be  general  because  hardly  enough  oxygen  is 
present  in  the  bulb  or  vaporizer.  Near  the  end  of  the  com- 
pression stroke,  however,  the  flame  strikes  out,  and  the  combus- 
tion becomes  explosive.  As  in  the  former  case,  the  vaporizer  is 
heated  by  a  lamp  at  the  start,  but  after  a  few  minutes  of  opera- 
tion the  walls  of  the  vaporizer,  if  well  protected,  remain  at  a  dull 
red  heat,  due  to  the  heat  of  compression  and  explosion. 


GAS  ENGINE  AUXILIARIES 


397 


Capitaine  *  employs  a  method  which  differs  from  that  used 
in  the  Hornsby  engine  in  that,  at  the  moment  the  fuel  is  injected 
into  the  vaporizer,  a  little  auxiliary  air  is  also  admitted  which 
sweeps  the  oil  vapor  formed  into  the  combustion  chamber  proper, 
where  it  meets  the  main  body  of  air  and  is  compressed  with  it. 
Ignition  ensues  from  the  hot  walls  of  the  vaporizer  as  in  the 
other  cases. 

4.  Ignition  by  Means  of  the  Electric  Spark.  —  Electric  Igni- 
tion is  to-day  used  more  than  any  other.  In  fact  in  some  branches 
of  the  industry,  automobile  work  for  instance,  it  is  used  exclu- 
sively. The  reasons  for  this  are  not  far  to  seek.  As  compared 
with  the  hot  tube,  there 
is  no  flame,  and  no  fuel 
required  to  feed  it.  The 
system  is  perfectly  flex- 
ible and  susceptible  of 
perfect  timing. 

There  are  a  number 
of  electric-ignition  sys- 
tems in  use,  differing 
in  their  methods  of 
wiring,  their  sources  of 
current,  etc.,  but  con- 
sidering for  the  moment  nothing  but  basic  principles,  all  the 
systems  may  be  grouped  under  two  heads.  These  are: 

1.  Make-and- Break  Ignition,  and 

2.  Jump-spark  Ignition. 

In  what  follows,  only  the  elementary  principles  of  electric 
ignition  will  be  discussed.  For  a  comprehensive  exposition  of 
the  subject,  consult  "Electric  Ignition  for  Motor  Vehicles"  by 
W.  Hibbert.f 

1.  MAKE-AND-BREAK  IGNITION.  —  The  simplest  kind  of  make- 
and- break  circuit  is  shown  in  diagram  in  Fig.  13-6.  J  In  this 
figure,  B  is  a  source  of  current  and  c  a  so-called  spark  coil.  In 
this  case  such  a  coil  consists  merely  of  a  number  of  turns  of 
comparatively  heavy  wire  wound  about  a  bundle  of  wrought- 

*  Zeitschrift  d.  V.  d.  I.,  1907,  p.  919. 

f  Whittaker  &  Co.,  64-66  Fifth  Ave.,  New  York  City. 

j  Roberts,  The  Gas  Engine  Handbook. 


FIG.  13-6.  — Make-and-Break  Circuit. 


398 


INTERNAL  COMBUSTION  ENGINES 


iron  wires.  This  coil  is  in  series  with  the  circuit,  and  acts  as 
an  inductive  resistance.  When  the  circuit  is  broken,  it  serves 
to  intensify  the  pressure,  causing  a  hot  spark  at  the  point  of 
break.  For  this  reason  the  writer  prefers  to  call  this  kind  of 
coil  an  intensifying  coil  rather  than  a  spark  coil,  which,  as  used 
in  jump-spark  ignition,  is  a  very  different  thing. 

The  make-and-break  mechanism  consists  in  this  case  of  a 
stationary  electrode,  e,  insulated  from  the  rest  of  the  engine,  and 
a  movable  electrode,  p.  The  latter  is  connected  to  a  flat  spring, 

S,  which  in  turn  is  in  contact 
with  the  cam,  C.  The  current 
Igniter  flows  from  B,  through  the  inten- 
sifying coil,  c,  to  the  electrode, 
p,  and  from  here  through  the 
electrode,  e,  back  to  5,  thus 
completing  the  circuit.  The 
operation  is  as  follows:  Cam  C, 
rotating  in  the  direction  of  the 
arrow,  first  presses  electrode  p 
against  electrode  e,  making  the 
circuit.  At  the  proper  moment, 
spring  S  slips  off  the  cam,  sud- 
denly forming  a  gap  between  p 
and  e,  across  which  the  spark 

jumps. 

Thig  Qf  make       d  break 

.  . 

mechanism    is    known    as    the 


FIG.  IJM.-Make-and-Break  Ignition 
Apparatus. 


hammer  break.  An  example  from  practice  is  shown  in  Fig. 
13-7.*  The  source  of  current  in  this  case  is  a  Bosch  magneto. 
The  current  flows  from  d  to  e,  the  stationary  electrode,  and  re- 
turns through  /,  the  movable  electrode,  and  the  forked  rod,  h. 
Actuated  by  a  latching  arrangement  on  the  half-time  shaft,  the 
armature  lever  is  pulled  to  the  left  about  20  degrees,  as  shown  in 
the  lower  figure.  This  puts  the  two  powerful  helical  springs 
shown  in  tension,  so  that  when  the  latch  releases,  the  armature 
sleeve  instantaneously  returns  to  its  normal  position,  generating 
the  required  current  by  cutting  the  lines  of  force  with  great 
rapidity.  At  the  same  instant  the  fork,  h,  strikes  the  bell  crank,  g, 
*  Giildner,  Verbrennungsmotoren,  p.  365. 


GAS  ENGINE  AUXILIARIES  399 

thus  separating  /  from  e,  and  causing  the  spark.  This  method 
is  susceptible  of  adjustment  by  regulating  the  time  of  release  of 
the  latch. 

It  should  be  noted  that  in  this  particular  instance  the  two 
electrodes  are  in  contact  until  the  spark  is  desired.  This  is  ad- 
missible because  with  the  source  of  current  used,  electric  energy 
is  generated  only  for  an  instant,  just  before  the  break.  If  a  con- 
tinuous source  of  current,  such  as  a  battery  for  instance,  is  used, 
it  becomes  necessary  to  modify  the  mechanism  so 'that  the  elec- 
trodes are  in  contact  only  for  a  short  time  before  the  break; 
otherwise  the  system  would  be  very  wasteful  of  current. 

The  hammer-break  mechanism  is  open  to  two  objections, 
rapid  wearing  away  of  the  points  and  fouling.  The  former 
is  aggravated  if  too  strong  a  current  is  used.  It  is  usual, 
therefore,  to  make  the  points  of  contact  of  some  metal  that  will 
not  easily  corrode  or  wear  away  under  heat.  Platinum,  or  plati- 
num-iridium  is  extensively  used  for  this  purpose.  There  are,  how- 
ever, some  special  alloys  on  the  market,  such-  as  Baker  &  Co.'s 
"Special,"  which  are  somewhat  less  costly,  but  do  the  work  fully 
as  well  or  better.  Platinum  is  practically  indestructible  by  heat, 
but  it  is  hardly  hard  enough  to  stand  the  wear.  The  only  remedy 
for  fouling  is  periodic  cleaning,  although  the  claim  is  made  for 
some  of  the  special  alloys  that  they  remain  bright  indefinitely. 

To  overcome  the  objection  of  fouling,  a  modification  of  the 
make-and-break  system  known  as  the  wipe  spark  is  sometimes 
employed.  In  this,  one  electrode  is  made  to  revolve  and  a  pro- 
jection on  it  "wipes"  across  the  other  electrode  at  the  proper 
time,  causing  a  spark  on  the  break.  The  spark  produced  in  this 
way  is  perhaps  hotter  than  that  formed  by  the  hammer  break, 
and  fouling  of  the  sparking  surfaces  is  effectually  prevented.  On 
the  other  hand,  the  wear  is  much  greater. 

Make-and-break  ignition  has  the  advantage  that  only  a  low 
voltage  is  required  to  operate  it.  The  pressure  ordinarily  used 
is  from  six  to  eight  volts,  while  in  many  cases  from  two  to  four 
volts  is  quite  sufficient.  There  is  thus  much  less  danger  from 
leakage  of  current  and  short-circuiting  in  this  system  than  there 
is  in  the  jump  spark  method. 

The  disadvantages  of  the  system  regarding  wrear  and  fouling 
have  been  already  pointed  out.  Another,  as  compared  with  the 


400 


INTERNAL  COMBUSTION  ENGINES 


jump  spark,  consists  in  the  fact  that  some  mechanically  operated 
gearing  is  required  to  "trip"  the  igniter.  Both  this  fact  and  the 
rapid  wear  of  the  contact  points  have  led  designers  to  adopt  the 
jump-spark  system  for  high  speed  work.  Lately,  however,  there 


high-speed  trip  gear. 


FIG.  13-8. —  Plan,  Fay  &  Bowen  Engine. 

seems  to  be  a  tendency  to  adapt  the  -make-and-break  system  also 
to  high  speeds,  caused  no  doubt  by  the  very  obvious  disadvantages 
of  the  jump  spark.     There  are  ways  of  efficiently  operating  a 
One  of  these,  used  by  the  Fay  &  Bowen 
Engine  Co.  for  medium 
high  speeds,  is  shown 
in  Figs.  13-8  and  13-9. 
Fig.  13-8  shows  a  plan 
view    of    the    vertical 
engine.      The    igniter 
shaft,   A,   passes    ver- 
tically    downward 
FIG.  13-9.-Igniter  Block,  Fay  &  Bowen  fa          h        h  _ 

Engine.  . 

jacket    space,    and    is 

driven  from  the  crank  shaft  by  a  pair  of  bevel  gears.  It 
runs  in  bronze  bearings,  and  where  it  passes  through  the 
jacket  it  is  encased  in  a  water-tight  tube.  At  the  top  this 
shaft  carries  a  small  gear  which  meshes  with  a  somewhat  larger 
gear,  B,  under  the  igniter  cam,  C.  All  the  gears  are  cut  gears 
and  run  practically  without  noise.  The  driving  is  positive  and 


GAS  ENGINE  AUXILIARIES  401 

there  can  be  no  slip.  As  the  cam,  C,  revolves,  it  engages  the 
plunger  D  and  forces  it  back  against  the  spring  G.  When  the 
plunger  slips  off  the  cam,  the  hammer,  E,  strikes  the  movable 
electrode,  F,  separating  it  from  the  stationary  electrode,  J,  caus- 
ing the  spark.  This  action  is  carried  out  with  the  same  rapidity 
no  matter  how  fast  the  fly-wheel  is  revolved  at  the  start.  For 
the  greater  part  of  its  revolution,  cam  C  is  not  in  contact  with  the 
plunger,  D,  and  hence  the  electrodes  are  separated,  thus  main- 
taining an  open  circuit  for  the  greater  part  of  the  time  and  pre- 
venting the  waste  of  current.  Just  as  soon  as  C  commences  to 
push  back  the  plunger  Z>,  the  spring  H  pulls  back  the  movable 
electrode  F,  and  contact  is  made  for  a  sufficient  length  of  time 
to  insure  a  good  flow  of  current. 

The  igniter  plug,  shown  in  greater  detail  in  Fig.  13-9,  is  en- 
tirely independent  of  the  driving  gear  and  is  held  in  place  by 
four  bolts,  which  can  be  removed  at  a  moment's  notice.  The 
seat  of  the  plug  is  a  ground  joint.  The  spark  points  can  there- 
fore be  examined  and  the  plug  replaced  in  a  very  short  time,  or 
a  new  plug  may  be  substituted  for  the  old  one.  The  chances  for 
wear  in  the  whole  arrangement,  however,  are  very  small  and 
there  seems  to  be  no  reason  why  this  igniter  gear  should  not  be 
used  for  speeds  much  higher  than  those  for  which  the  designers 
now  use  it.  Adjustment  of  the  spark  in  this  gear  is  made  in  a 
very  simple  way  by  pivoting  the  gear  B  about  the  center  of  the 
shaft  A,  thus  changing  the  position  of  the  cam,  C,  with  relation 
to  the  plunger.  The  adjustment  is  controlled  by  the  hand  lever 
shown.  Should  the  lever  by  any  accident  be  left  in  the  advanced 
spark  position,  so  that  the  engine  may  get  an  explosion  turning 
it  the  wrong  way  the  next  time  it  is  started,  a  small  clutch  located 
under  the  igniter  cam,  C,  immediately  frees  the  cam  so  that  no 
second  back  explosion  can  take  place. 

2.  JUMP  SPARK  IGNITION.  —  Figure  13-10*  shows  diagram- 
matically  the  simplest  type  of  jump-spark  system.  There  are 
in  all  cases  a  primary  or  low-tension  and  a  secondary  or  high- 
tension  circuit.  The  primary  circuit  is  shown  in  heavy  line  and 
contains  the  source  of  current,  B.  The  current  flows  from  B 
through  an  arrangement,  T,  called  the  interrupter,  commutator, 
or  timer,  which  serves  to  make  and  break  the  primary  current  at 
*  T.  H.  White,  Petrol  Motors  and  Motor  Cars. 


402 


INTERNAL  COMBUSTION  ENGINES 


the  proper  time.  It  then  passes  through  the  primary  winding,  P, 
of  the  spark  coil  and  returns  to  the  source,  completing  the  primary 
circuit.  The  secondary  circuit,  shown  by  a  light  line,  consists 
of  the  secondary  winding,  S,  of  the  spark  coil  and  a  spark  plug  in 
the  cylinder  of  the  engine,  indicated  in  the  figure  by  Z.  It  should 
be  noted,  in  connection  with  the  secondary  circuit,  that  this  cir- 
cuit is  never  actually  closed,  since  a  spark  gap  always  exists  in 
the  spark  plug.  Hence  current  cannot  be  said  to  flow  in  this 
circuit  until  the  tension  or  voltage  becomes  high  enough  to  bridge 
this  gap  by  a  spark. 

To  understand  the  operation  of  the  jump-spark  system  it  is 
necessary  first  to  study  the  action  of  the  spark  coil.  There  are 

two  kinds  of  these  coils,  the 
non-trembler  and  the  trem- 
bler coil. 

The  former  is  the  type 
indicated  in  Fig.  13-10.  Its 
actual  construction  is  about 
a.s  follows:  /  is  the  core  of 
the  coil  consisting  of  a  bun- 
dle of  fine  iron  wires.  This 
is  covered  with  a  layer  of 
some  insulating  material, 

io_in  and   around   this   is  wound 

.  13-10.  —  Simple  Jump-spark  System. 

the  primary -winding.  This 

consists  generally  of  several  layers  of  insulated  copper  wire, 
about  No.  20  or  22.  A  light  layer  of  insulation  next  sepa- 
rates this  from  the  secondary  winding,  which  consists  generally 
of  some  10  to  15000  turns  of  very  fine  insulated  wire.  Each 
layer- of  this  wire  is  separated  from  the  next  by  a  layer  of  insula- 
tion to  prevent  short-circuiting  under  the  very  high  pressures 
occurring. 

To  understand  easily  what  follows,  it  is  necessary  merely  to 
remember  that  if  any  conductor  of  electricity  is  moved  across  a 
magnetic  field,  or  if  a  magnetic  field  is  moved  across  a  conductor, 
an  electric  current  will  immediately  be  set  up  in  this  conductor. 
Further,  that  if  a  current  be  passed  through  a  conductor,  a  mag- 
netic field  will  immediately  be  set  up  around  the  conductor. 

Now,  in  the  spark  coil  described,  a  current  is  sent  through  the 


GAS  ENGINE  AUXILIARIES 


403 


primary  winding  as  soon  as  the  contact  is  closed  at  T.  This 
converts  the  iron  core  of  the  coil  into  an  electro-magnet,  setting 
up  a  strong  magnetic  field.  The  magnetic  lines  move  outward 
across  the  windings  of  the  secondary  circuit  and  induce  a  high 
tension  in  this  circuit.  But,  owing  to  self-induction,  the  build- 
ing up  of  the  magnetic  field  is  much  slower  than  the  collapse  of 
the  field  when  the  primary  current  is  suddenly  interrupted  at  T. 
The  magnetic  lines  then  move  inward  across  the  secondary  wind- 
ing with  much  greater  rapidity,  hence  the  pressure  induced  is 
much  higher  than  that  existing  during  the  building  up  of  the  field, 
and,  if  the  spark  plug  is  right  for  the  coil,  a  spark  will  bridge 
across  the  gap  in  the  cylinder,  igniting  the  charge.  The  fact  that 


FIG.  13—11.  —  Jump-spark  System  with  Trembler  Coil. 

the  voltage  induced  on  the  making  of  the  current  is  not  high 
enough  to  bridge  the  gap  prevents  the  occurrence  of  a  double 
spark  in  the  cylinder,  which  might  lead  to  pre-ignition  of  the 
charge. 

Since  with  the  non-trembler  coil  the  current  in  the  primary 
is  established  only  once  when  ignition  is  desired,  only  a  single 
spark  will  occur  in  the  cylinder.  It  is  possible  that  this  single 
spark  may  fail  to  fire  and  a  series  of  sparks  at  the  time  of  ignition 
is  hence  an  advantage.  This  has  led  to  the  adoption  of  the 
trembler  coil,  Fig.  13-11*.  The  circuit  shown  in  this  figure  is 
the  same  as  that  of  Fig.  13-10,  except  that  a  trembler  or  "  buzzer  " 
T  and  a  timer  or  commutator  W  have  been  substituted  for  the 

*  T.  H.  White,  Petrol  Motor  and  Motor  Cars. 


404  INTERNAL  COMBUSTION  ENGINES 

simple  make-and-break  mechanism,  T,  of  Fig.  13-10.  The 
action  of  the  trembler  is  simple.  As  soon  as  W  makes  contact, 
the  primary  current  converts  the  core,  /,  into  an  electro-magnet 
which  attracts  the  armature,  A,  of  the  trembler  blade.  This 
action,  however,  breaks  the  primary  current  by  pulling  the 
spring  blade,  T,  away  from  the  constant  screw  at  E.  A  spark 
then  jumps  over  in  the  cylinder  as  before  explained.  The  break- 
ing of  the  primary  current,  however,  releases  the  armature,  A,' 
which  returns  to  its  normal  position,  again  establishing  the  pri- 
mary circuit  at  E.  The  operation  is  then  repeated.  This  action 
establishes  a  pulsating  pressure  in  the  secondary  winding,  causing 
a  series  of  sparks  as  long  as  contact  is  maintained  at  W. 

The  advantage  of  the  trembler  coil  has  already  been  pointed 
out.  The  disadvantages  exist  in  the  fact  that  a  second  moving 
part  is  introduced  into  the  primary  circuit  which  must  be  kept 
carefully  adjusted  if  the  system  is  to  work  satisfactorily. 

In  both  Figs.  13-10  and  13-11  it  will  be  noticed  that  there 
is  an  arrangement,  C,  called  a  condenser,  connected  across  the 
make-and-break  mechanism,  in  the  non-trembler  coil  across  the 
interrupter,  in  the  trembler  coil  across  the  vibrator  or  buzzer. 
The  condenser  consists  of  a  large  number  of  sheets  of  tinfoil,  the 
number  depending  upon  the  capacity  desired.  Each  sheet  is 
separated  from  the  next  by  a  layer  of  insulation,  and  the  alternate 
sheets  are  connected  together.  This  manner  of  construction  is 
clearly  shown  in  the  diagram.  The  object  of  the  condenser  is  to 
prevent  serious  sparking  at  the  make-and-break  contacts  in  the 
primary  circuit.  The  reasons  why  such  a  spark  occurs  at  all  in 
such  a  circuit  is  that  the  collapse  of  the  magnetic  field  not  only 
induces  a  high  pressure  in  the  secondary  winding,  but  also  causes 
a  momentary  increase  in  the  pressure  in  the  primary,  thus  bridg- 
ing any  small  gap  by  a  spark,  and  causing  rapid  wear  of  the  con- 
tact points  of  the  trembler  at  E,  Fig.  13-11.  When  the  primary 
circuit  is  now  broken  at  E,  the  current  induced,  instead  of  jump- 
ing across,  is  expended  in  charging  the  condenser.  The  action 
is  very  similar  to  that  of  an  air  chamber  on  a  hydraulic  pipe  line, 
absorbing  shock  by  compressing  air.  The  next  time  the  primary 
circuit  is  closed  at  E,  the  condenser  discharges  and  helps  to  send 
a  current  through  the  primary. 

As  actually  constructed,  spark  coils  are  very  compact.     The 


GAS  ENGINE  AUXILIARIES 


405 


condenser  is  generally  placed  under  the  coils,  and  the  whole  is 
enclosed  in  a  tight  wooden  box.  Externally  nothing  shows  but 
the  terminals  and  the  trembler,  if  the  coil  is  of  that  type.  In 


FIG.  13-12.  — Three-Terminal  Spark  Coil. 

some-  coils  one  end  of  the  secondary  coil  is  connected  to  one  end 
of  the  primary  winding,  so  that  only  three  terminals  show,  as  in 
Fig.  13-12.  Fig.  13-13  shows  a  four-terminal  coil,  the  secondary 
terminals  being  on 
top.  The  tremblers 
are  of  various  con- 
structions, nearly  each 
maker  having  his  own 
design.  They  must 
give  a  quick  break. 
They  should  be  easy 
of  fine  adjustment, 
but  the  adjustment, 
once  made,  should 
stay.  In  many  cases, 

as  for  automobile  and  FlG  13_13  _  Four.Terminal  Coil. 

marine   purposes,  the 

entire  spark  coil  is  enclosed  in  a  second  box  with  tight  cover,  so 
as  to  prevent  fouling  by  mud  or  water.  An  example  of  this  is 
shown  in  Fig.  13-14. 

Timers.  —  A  very  important  part  of  a  jump-spark  system  is 
the  device  making  and  breaking  the  primary  circuit,  for  every- 
thing depends  upon  the  non-failing  regularity  of  its  performance. 


406 


INTERNAL  COMBUSTION  ENGINES 


13-14.  —  Dash-board  Coil. 


There  is  a  large  number  of  such  timers  or  commutators  on  the 
market,  all  more  or  less  good.     Figs.  13-15  to  13-18  show  a  few 

of  the  designs.  The  fundamental 
idea  in  all  of  these  is  the  same. 
The  half-time  shaft  actuates  a  cam 
or  wiper  inside  of  a  case,  which 
cam,  at  the  proper  time,  makes  and 
breaks  contact  with  insulated  ter- 
minals held  by  the  surrounding  case. 
The  number  of  such  terminals  de- 
pends upon  the  number  of  cylin- 
ders. A  great  deal  of  ingenuity  is 
shown  in  the  prevention  of  friction 
between  the  cam  and  the  terminal. 
The  action  of  the  Sintz  timer,  Fig. 
13-15,  is  obvious.  Here  we  have 
roller  contact,  the  ends  of  the  ter- 
minals, are  hardened  steel,  and  the 
case  is  dust  proof.  Of  somewhat 
similar, design  is  the  Lacoste  timer, 
Fig.  13-16.  The  cross-section  shows  clearly  the  manner  of  con- 
struction. Somewhat  more  complicated,  but  of  excellent  design, 
is  the  Pittsfield  timer,  Fig.  13-17.  In 
the  Grouse-Hinds  double  ball  timer, 
Fig.  13-18,  the  cam  on  the  half-time 
shaft  passes  between  two  steel  balls, 
held  as  shown.  This  makes  the  con- 
tact positive,  keeps  the  surfaces 
clean,  and  the  wear  is  very  small. 

With  any  of  the  above  devices, 
the  time  of  sparking  may  be  varied 
by  shifting  the  terminals  with  ref- 
erence to  the  cam  or  wiper  on  the 
half-time  shaft.  Some  timers  incor- 
porate governors  to  automatically 
time  the  spark. 

Spark  Plugs.  —  A  spark  plug  consists  of  two  electrodes  or 
sparking  points  which  are  held  a  certain  distance  apart  in  the 
cylinder.  The  central  electrode  is  insulated,  while  the  metallic 


FIG.  13-15.  —  Sintz  Timer. 


GAS  ENGINE  AUXILIARIES 


407 


jacket  enclosing  the  insulation  generally  carries  the  other  spark 
point.  This  point,  therefore,  can  be  put  in  the  circuit  by  fastening 
a  wire  anywhere  to  the  engine.  The  essential  requirements  of 

I 


FIG.  13-16.  —  Lacoste  Timer. 


FIG.  13-17.  —  Pittsfield  Timer. 

the  construction  are  that  the  insulation  of  the  central  electrode 
be  sufficient  and  not  liable  to  breaking  down,  and  that  the  elec- 
trode points  be  so  constructed  that  the  plug  is  not  easily  subject 
to  fouling. 


408 


INTERNAL  COMBUSTION  ENGINES 


The  most  important   part  of  the  entire  plug  is  perhaps  the 
insulation  of  the  central   electrode.     Among  the  materials  used 

for  this  purpose, 
porcelain  and  mica 
take  the  lead.  Por- 
celain, while  excel- 
lent, is  very  liable 
to  break  under  any 
uneven  expansion  by 
heat,  and  the  insu- 
lation must  therefore 
be  carefully  designed 
with  this  point  in 
view.  Mica  is  not 
open  to  that  objec- 
tion and  its  electri- 
cal resistance  is  very 
high,  but  owing  to 
its  laminated  struc- 
ture, oil  or  soot 
may  after  a  time  be 
forced  between  the 


laminations    under 


Fi«.  -13-18.  —  Grouse-Hinds  Double  Ball  Timer. 

the  high  pressures  existing, 
thus  short-circuiting  the  plug. 

How  various  manufacturers 
have  tried  to  take  into  account 
the  requirements  mentioned,  is 
shown  in  Fig.  13-19.*  The 
first  six  plugs  there  shown  have 
porcelain,  and  the  last  two  mica 
insulation. 

It  should  be  remembered  in 
connection  with  spark  plugs,  that 
since  the  electrical  resistance 
across  the  spark  gap  is  greater 
when  in  actual  operation  in  the 

engine  than  when   in  ordinary    T?          m     tr    • 

ai-y     FIG.  13-19.  — Various  Designs  of  Spark 
air,  a  plug  may  give  a  fair  spark  piugs< 

*  From  Romans,  Automobiles,  p.  284. 


GAS  ENGINE  AUXILIARIES  409 

when  tested  in  air,  and  may  still  fail  in  operation.  It  should  also 
be  remembered  that  heat  will  lower  the  electrical  resistance  of 
porcelain,  so  that  when  the  plug  is  very  hot,  short-circuiting 
through  the  insulation  may  result.  It  has  been  shown  by  ex- 
periment that  while  the  resistance  of  porcelain  cold  was  about 
100  megohms,  this  fell  to  2  megohms  when  the  plug  was  at  a 
dull  red  heat  and  under  this  condition  sparking  ceased.  The 
spark,  however,  was  immediately  restored  by  an  external  spark 
gap,  and  continued  even  when  the  resistance  had  fallen  to  800,000 
ohms.  Without  the  external  gap,  if  the  plug  was  allowed  to 
cool  down,  sparking  recommenced  when  the  resistance  of  the 
porcelain  had  again  risen  to  5  megohms. 

Auxiliary    Spark    Gap.  —  As   the    name    implies,    this   is    a 
second  spark  gap  placed  in  the  secondary  circuit  outside  of  the 


FIG.  13-20.  —  Auxiliary  Spark-gap. 

cylinder.  This  gap  acts  like  an  electrical  condenser,  above 
explained.  The  pressure  builds  up  on  one  of  the  terminals  of  this 
gap,  until  it  is  high  enough  to  break  through  the  intervening  air, 
causing  an  impulse  of  very  high  pressure  through  the  circuit,  thus 
giving  a  good  spark  across  the  main  gap  in  the  cylinder.  Fig. 
13-20.*  shows  one  form  of  auxiliary  spark  gap.  The  advantages 
claimed  for  the  device  are: 

(a)  Greater  certainty  of  sparking  in  the  cylinder,  since  the 
higher  pressure  generated  will  cause  a  spark  even  across  a  par- 
tially fouled  plug. 

(b)  Greater  life  of  battery,  since  current  cannot  leap  across 
a  fouled  plug  as  long  as  the  auxiliary  gap  is  not  bridged. 

(c)  The  sparking  can  be  watched,  since  a  spark  across  the  gap 
always  means  a  spark  in  the  cylinder. 

*  Homans,  Automobiles,  p.  290. 


410  INTERNAL  COMBUSTION  ENGINES 

In  spite  of  these  facts  the  auxiliary  spark  gap  has  not  found 
extended  application. 

RELATIVE  ADVANTAGES  AND  DISADVANTAGES  OF    MAKE-AND-BREAK 
AND    JUMP-SPARK    SYSTEMS 

Make  and  Break  Ignition.  —  Low  tension  throughout  the  cir- 
cuit, requiring  less  thorough  insulation,  and  causing  less  trouble 
from  short-circuiting.  The  system  is  electrically  more  simple, 
while  mechanically  it  is  somewhat  more  complex  than  the  jump- 
spark  system.  This  latter  fact  makes  it  somewhat  difficult  to 
apply  to  high-speed  engines. 

Jump-spark  Ignition.  —  Electrically  more  complex  than  the 
other,  but  has  no  moving  parts  inside  of  the  cylinder. 

Can  be  operated  under  very  high-speeds  with  entire  success, 
and  has  the  greatest  flexibility  with  regard  to  spark  adjustment. 

Sources  of  Current.  —  All  sources  of  electrical  current  used 
for  electric  ignition  may  be  classed  under  two  heads: 

1.  Chemical  Generators,  under  which  come 

(a)  Primary  sources,  as  wet  and  dry  cells,  and 

(6)  Secondary  sources,  as  the  storage  battery  or  accumulator. 

2.  Mechanical    Generators,    variously    called    dynamos    and 
magnetos. 

1.    Chemical  Sources  of  Current. 

(a)  WET  AND  DRY  CELLS.  —  All  chemical  cells  consist  of 
three  essential  parts,  a  positive  and  a  negative  electrode  and  an 
exciting  liquid,  called  the  electrolyte.  As  the  name  implies,  in 
the  wet  cell  this  electrolyte  is  used  in  its  liquid  form,  while  in  the 
dry  cell  it  is  mixed  with  some  absorbing  material,  and  the  paste 
is  used  to  fill  the  space  between  the  electrodes.  Take  the  dry 
cell  as  an  example.  The  negative  element  is  usually  a  carbon 
rod  placed  at  the  center  of  the  circular  case  which  forms  the 
envelope  of  the  cell.  This  rod  is  surrounded  generally  first  by 
a  layer  of  manganese  dioxide,  the  purpose  of  which  will  appear 
later,  and  the  rest  of  the  space  between  this  and  the  positive 
element,  usually  zinc  in  the  shape  of  a  cylinder,  is  then  filled 
with  the  electrolyte  paste,  the  original  liquid  being  usually  sal- 
ammoniac  and  water.  The  top  of  the  cell  is  then  covered  with 
pitch  or  other  substance  that  prevents  the  evaporation  of  the 
liquid  in  the  paste,  except  that  a  small  vent  hole  is  left  to  allow 


GAS  ENGINE  AUXILIARIES  411 

of  the  escape  of  any  gas  that  may  form  within  the  cell  due  to  the 
chemical  action  going  on.  In  such  a  cell  the  current  generated 
by  the  action  of  the  electrolyte  passes  from  the  zinc  to  the  carbon 
electrode,  so  that  as  far  as  the  terminals  of  the  cell  are  concerned, 
the  carbon  is  the  positive  terminal.  The  chemical  action  destroys 
the  zinc  after  a  time  and  produces  hydrogen  gas  on  the  carbon 
element.  The  greater  the  amount  of  this  gas  deposited  on  this 
element,  the  slower  the  generation  of  current,  so  that  it  may 
finally  cease  altogether.  The  cell  is  then  said  to  be  polarized. 
In  dry  cells  the  gas  is  taken  care  of  in  two  ways;  the  vent  hole 
in  the  top  allows  some  of  it  to  escape,  while  the  layer  of  man- 
ganese dioxide  above  mentioned  absorbs  another  part.  But  it 
is  a  fact  that  by  these  means  not  all  of  the  gas  is  rendered  harm- 
less and  hence  the  cells  will  polarize  with  more  or  less  rapidity. 
This  merely  means  that  if  current  is  drawn  from  them  continu- 
ously for  any  considerable  length  of  time,  their  strength  will  fail, 
making  the  cell  appear  dead.  The  same  reasoning  applies  to 
wet  cells  where  the  hydrogen  is  allowed  to  escape  through  the 
liquid.  Now,  assuming  that  the  zinc  is  not  yet  destroyed,  if  a 
cell  so  polarized  is  allowed  to  recuperate,  it  will  again  attain 
nearly  its  normal  strength  and  may  be  used  as  before.  The  cells 
are  said  to  be  adapted  to  "open-circuit  work.'7  From  all  of  this 
it  is  quite  evident  that  in  places  where  the  requirement  for  current 
is  not  very  great  and,  above  all,  not  continuous,  the  primary  cell 
will  give  satisfactory  service.  But  where  the  draft  of  current  is 
nearly  continuous,  as  in  high-speed  four-cylinder  machines  for 
instance,  the  cell  will  rapidly  polarize  and  soon  fail  to  give  suffi- 
cient voltage  to  operate  the  spark  coil.  The  average  size  of  a 
dry  cell  is  about  2%"  x  7" '.  It  will  give  when  fresh  from  1.3  to 
1.5  .volts  and  from  12  to  15  amperes. 

It  should  be  understood  that  there  are  other  combinations  of 
electrodes  and  electrolytes  which  may  be  used  to  generate  cur- 
rent. Thus  the  so-called  soda-cell  is  made  up  of  a  zinc  plate  and  a 
copper-oxide  plate  with  a  caustic  soda  solution  as  the  electrolyte. 

(b)  STORAGE  BATTERIES  OR  ACCUMULATORS.  —  A  storage  cell, 
like  a  primary  cell,  consists  of  two  electrodes  dipped  in  an  elec- 
trolyte, but  contrary  to  the  primary  cell,  it  cannot  give  off  elec- 
trical energy  in  its  original  state  when  the  circuit  is  closed.  It  is 
necessary  to  charge  a  storage  cell  before  it  can  return  electrical 


412  INTERNAL  COMBUSTION  ENGINES 

energy  on  the  discharge.  The  charging  action  causes  chemical 
changes  in  the  material  of  the  electrodes  and  in  the  electrolyte. 
The  energy  so  rendered  latent  is  nearly  all  restored,  when,  after 
the  charging  current  is  disconnected,  the  outside  circuit  is  closed. 
Chemical  changes,  producing  a  current  in  the  reverse  direction, 
then  take  place  in  the  cell,  which  return  both  the  electrodes  and 
the  electrolyte  to  their  original  condition.  Some  exhausted 
primary  cells  may  be  partially  restored  by  passing  a  current 
through  them  in  the  reverse  way,  but  in  most  cases  the  trouble 
is  not  worth  while.  The  possibility  of  a  nearly  complete  re- 
generation of  a  storage  cell  is  the  chief  difference  between  it  and 
a  primary  cell. 

There  are  a  number  of  materials  which  can  be  used  as  elec- 
trodes and  electrolytes,  but  the  usual  type  of  storage  cell  to-day 
is  that  using  some  lead  compound  for  the  former  and  sulfuric  acid 
and  water  for  the  latter.  Hence  only  this  lead  storage  cell  will 
be  here  considered. 

In  its  modern  form,  both  the  positive  and  negative  plates  of 
a  cell  consist  of  cast  grids  of  lead,  to  which  antimony  is  sometimes 
added  to  stiffen  them.  The  perforations  in  the  positive  plate  are 
first  filled  with  some  compound  of  lead,  as  Pb3O4,  which  is  after- 
ward converted  to  peroxide  of  lead,  PbO2.  Similarly  the  negative 
plate  is  filled  with  PbO  which  is  afterwards  converted  into  spongy 
metallic  lead.  A  number  of  plates  so  prepared  are  then  placed 
side  by  side  in  a  glass  jar,  or  if  the  battery  is  to  be  used  for  auto- 
mobile work,  in  a  vessel  of  hard  rubber  or  of  wood  lined  with 
rubber  or  lead.  Positive  and  negative  plates  alternate,  and  all 
the  plates  of  like  kind  are  connected  together.  There  should 
always  be  one  more  negative  than  positive  plates  so  that  each 
side  of,  each  positive  plate  shall  face  a  negative  plate.  The 
arrangement  of  plates  presents  a  large  plate  surface  in  a  compact 
space.  Suitable  insulation  separates  the  plates  from  each  other 
and  keeps  them  from  touching  the  bottom,  in  order  to  prevent 
any  short-circuiting  by  contact  or  by  dipping  into  any  sediment 
that  may  form.  In  automobile  batteries,  the  top  is  enclosed  to 
prevent  the  spilling  of  the  electrolyte,  and  nothing  shows  but  the 
two  terminals  and  an  opening  for  filling.  This  is  usually  kept 
closed  by  a  rubber  cork  with  a  small  vent  hole  to  allow  of  the 
escape  of  any  gases  that  may  form. 


GAS  ENGINE  AUXILIARIES  413 

The  chemical  reactions  that  occur  during  charging  and  dis- 
charging are  not  yet  fully  understood,  but  it  is  agreed  that  the 
main  action  is  the  formation  of  lead  peroxide  on  the  positive  and 
metallic  lead  on  the  negative  plate  during  charging,  and  the  for- 
mation of  lead  sulphate  on  both  plates  during  discharge.  The 
action  is  best  explained  by  the  following  diagram.* 

Discharging  >- 

Charged  Condition  Discharged  Condition 

+  Plate,  Electrolyte,  -  Plate,      +  Plate  -  Plate 

PbO2     +2H2SO4+Pb    =     PbSO4     +  2H2O  +  PbSO4+ electric  energy 

•< Charging 

Such  a  lead  cell  when  fully  charged  should  show  a  voltage  of 
from  2.2  to  2.25  on  open  circuit,  and  from  2.10  to  2.15  when  the 
engine  is  running.  The  voltage  soon  drops  to  2.0  and  then  slowly 
to  1.8.  Three-quarters  of  the  total  discharge  takes  place  between 
the  latter  figures.  It  is  usual  to  discontinue  discharging  a  cell 
when  the  voltage  has  reached  1.75.  Beyond  this  point  the 
formation  of  the  insoluble  lead  sulfate  becomes  troublesome  and, 
discharging  much  below  this  figure,  the  cell  may  be  destroyed  or 
at  least  seriously  impaired. 

Rating  of  Storage  Batteries.  —  The  amperage  of  storage 
cells  depends  on  the  weight  of  material  in  the  cell  converted  by 
the  chemical  reactions,  while  the  rate  at  which  electrical  energy 
can  be  taken  off  depends  upon  the  surface  of  the  active  materials 
exposed  to  chemical  action.  Cells  are  rated  by  their  ampere- 
hour  capacity  and  nearly  every  maker  states  the  normal  rate  of 
discharge  recommended.  For  ordinary  constructions  the  nor- 
mal discharge  rate  is  about  .04  ampere  per  square  inch  of  total 
positive  plate  surface,  and  the  discharge  capacity  about  4  ampere- 
hours  per  pound  of  plate,  including  negative  and  positive.  In 
order  to  be  able  to  compare  different  cells,  the  capacity  rating  is 
based  upon  a  current  that  will  cause  the  voltage  of  the  cell  to  fall 
to  1.75  volts  in  eight  hours.  Thus,  if  to  produce  this  result  a 
current  of  say  25  amperes  must  be  drawn,  the  capacity  of  the 
cell  is  said  to  be  8  x  25  =  200  ampere-hours.  If  the  rate  of  dis- 
charge is  faster  than  this,  it  is  obtained  at  the  expense  of  capacity. 
Thus  if  a  current  of  40  amperes  were  drawn,  the  capacity  might- 

*  International  Library  of  Technology. 


414  INTERNAL  COMBUSTION  ENGINES 

be  only  160  ampere-hours.  Conversely,  if  the  rate  of  discharge 
is  slower  than  the  standard,  the  limiting  voltage  of  1.75  may  not 
be  reached  for  say  twelve  hours  instead  of  eight.  These  varia- 
tions depend  largely  upon  the  make  of  cell. 

Charging  a  Cell.  —  In  charging  a  cell  it  is  absolutely  neces- 
sary to  determine  the  polarity  of  the  terminals  of  the  source  of 
current.  The  positive  terminal  must  be  connected  to  the  posi- 
tive terminal  of  the  cell.  The  charging  rate  of  lead  cells  should 
be  about  the  same  as  the  normal  eight-hour  discharge  rate.  It 
is,  however,  possible  to  use  smaller  currents  for  a  longer  time. 
The  voltage  of  the  charging  current  must  be  somewhat  greater, 
from  5  to  10  per  cent,  than  the  discharge  voltage,  on  account  of 
the  internal  resistance  that  must  be  overcome.  In  one  charging 
test,  the  charging  voltage  rose  from  2.05  to  2.15  at  the  end 
of  two  hours,  to  2.20  at  the  end  of  six  hours,  and  to  2.50  volts  in 
eight  hours  and  forty-five  minutes.  The  rate  of  charging  was 
thus  about  normal.  If  charging  is  continued  beyond  this  point, 
the  electrolyte  will  have  the  appearance  of  boiling,  owing  to  the 
gas  that  is  being  evolved.  Slight  overcharging  will  not  injure  a 
cell,  but  a  large  amount  of  it  leads  to  sulfating  and  permanent 
injury. 

Testing  of  Storage  Batteries.  —  Two  tests  may  be  made, 
one  for  voltage,  the  other  for  sparking.  For  the  former  a  low- 
reading  voltmeter,  0  to  3  volts,  is  connected  across  the  terminals 
of  the  battery,  while  the  engine  is  in  operation.  The  reading 
should  be  above  1.75  volts.  Any  cell  may  give  1.9  to  2  volts  on 
open  circuit,  even  if  completely  run  down  a  short  time  before. 
The  sparking  test  is  made  to  determine  in  a  way  the  state  of  the 
charge  by  noting  the  kind  of  spark.  This  test  should  be  care- 
fully done  and  not  repeated  too  often.  It  is  a  dead  short-circuit 
method  and  therefore  not  good  for  the  cell.  The  use  of  an 
ammeter  is  for  that  reason  not  recommended,  as  it  would  take  too 
long  to  get  a  reading.  The  sparking  test  is  made  by  placing  one 
skinned  end  of  a  piece  of  insulated  copper  wire  in  contact  with 
one  end  binding  post  of  the  battery,  and  then  drawing  the  other 
end  rapidly  across  the  other  post.  The  spark  should  be  loud 
and  snappy. 

Any  storage  battery  should  last  from  three  to  four  years  if 
properly  treated.  It  is  well  to  adopt  a  regular  charging  period, 


GAS  ENGINE  AUXILIARIES  415 

say  once  in  three  weeks  for  the  ordinary  automobile  battery, 
whether  the  battery  is  run  down  or  not. 

2.  Mechanical  Forms  of  Generators:  Dynamos  and  Magnetos. 
-  Mechanical  forms  of  current  producers  have  the  advantage 
over  primary  and  secondary  batteries  in  that  the  energy  required 
by  them  is  derived  directly  from  the  engine  they  operate.  Hence 
current  will  be  produced  as  long  as  and  only  when  desired.  The 
other  forms  of  generators  depend  upon  sources  of  energy  entirely 
extraneous  to  the  engine  plant,  and  the  supply  of  current  is  there- 
fore not  in  any  sense  automatic,  which  would  be  the  ideal  condi- 
tion. The  terms  dynamo  and  magneto  have  been  variously 
used.  Some  writers  designate  by  "  dynamo  "  any  generator  hav- 
ing electro-magnets  serving  to  establish  the  magnetic  field,  and 
by  "magneto"  any  machine  employing  permanent  magnets  for 
this  service.  Others  define  the  difference  as  existing  in  the  kind 
of  current  produced,  a  dynamo  furnishing  direct,  i.e.,  continuous 
current,  while  a  magneto  produces  alternating,  i.e.,  pulsating, 
current.  Whatever  definition  is  adhered  to,  it  should  be  remem- 
bered that  in  either  machine  the  current  is  produced  by  an 
electrical  conductor  cutting  the  magnetic  field.  The  current  is  pro- 
duced in  exactly  the  same  way,  and  for  exactly  the  same  reason, 
as  that  established  in  the  secondary  winding  of  a  spark  coil,  as 
explained  above.  In  this  case  the  conductor  of  electricity  is 
wound  upon  a  piece  of  metal,  called  an  armature,  which  is  rapidly 
rotated  in  a  magnetic  field.  It  makes  no  difference  whether  this 
field  is  produced  by  permanent  magnets  or  by  electro-magnets. 
If  there  are  a  number  of  such  conductors  upon  the  armature,  and 
the  current  induced  in  each  is  properly  collected  by  a  so-called 
commutator  upon  the  armature  shaft  so  as  to  be  practically  con- 
tinuous in  its  flow  through  the  external  circuit,  we  have  what  is 
generally  called  a  dynamo.  On  the  other  hand,  if  the  current 
in  the  external  circuit  rises  to  a  maximum  value  and  then  dies 
out  to  give  a  maximum  value  next  in  the  opposite  direction,  the 
machine  is  generally  known  as  a  magneto.  While  in  all  dynamos 
and  most  magnetos  the  armature  constantly  rotates  in  one  direc- 
tion, it  should  be  stated  that  in  all  magnetos  this  is  not  at  all 
necessary.  Thus  in  the  Simms  Bosch  magneto,  the  armature  is 
stationary,  and  only  a  sleeve  surrounding  the  armature  is  rapidly 
oscillated  in  the  magnetic '  field,  It  would  be  beyond  the  scope 


416 


INTERNAL  COMBUSTION  ENGINES 


of  this  book,  however,  to  discuss  all  the  possible  modifications, 
and  the  reader  is  hence  referred  to  the  works  upon  this  subject.* 
In  general,  the  small  dynamo  used  for  ignition  purposes  is 
driven  by  means  of  a  friction  wheel  from  the  fly-wheel  of  the 
engine.  There  is  then  no  current  available  from  the  dynamo  when 
the  engine  is  started,  and  it  becomes  necessary  to  use  a  battery 
of  some  kind  for  the  first  minute  or  two,  switching  in  the  dynamo 
when  it  is  up  to  speed.  This  scheme  has  the  disadvantage  that 
the  battery  is  sometimes  left  in  the  circuit  and  the  dynamos  have 
been  known  to  burn  out  under  excessive  engine  speeds.  A  device 
called  the  Auto  Sparker,  Fig.  13-21,  overcomes  these  difficulties. 
This  little  dynamo  is  fitted  with  a  centrifugal  governor  which 

controls  the  position  of 
the  friction  wheel  on  the 
fly-wheel  rim,  so  that 
even  at  starting  the  ar- 
mature rotates  rapidly 
enough  to  furnish  start- 
ing current.  This  does 
away  with  an  auxiliary 
battery.  As  the  engine 
speeds  up,  the  governor 


FIG.  13-21.  —  Auto  Sparker. 


of  the  dynamo  acts  to 
keep  the  armature  speed 
constant,  independent  of  the  diameter  of  the  fly-wheel  or  the 
engine  speed.  By  adjusting  the  governor  tension  spring,  it  is 
possible  to  control  the  speed  of  the  dynamo  to  get  any  current 
between  1  and  3  amperes  and  any  voltage  between  3  and  10  volts. 
Regarding  magnetos,  the  following  description  of  the  action 
of  a  magneto,  together  with  the  explanation  of  the  method  of 
connecting  it  up,  is  taken  from  a  catalogue  of  the  Holley  Bros. 
Company  of  Detroit.  For  clearness  and  simplicity  this  descrip- 
tion can  hardly  be  improved  upon. 

"A  magneto,  so  far  as  its  essential  parts  are  concerned,  is  a 
very  simple  thing.  It  consists  of  a  U-shaped  piece  of  special 
steel,  which  is  permanently  magnetized;  in  other  words,  a  com- 
mon horseshoe  magnet  and  a  rotating  armature.  The  armature 
consists  of  a  soft  iron  core  of  approximate  H  cross-section  as 
*  W.  Hibbert,  Electric  Ignition  for  Motor  Vehicles. 


GAS  ENGINE  AUXILIARIES 


417 


viewed  along  the  shaft  upon  which  it  is  supported  and  on  which 
it  is  designed  to  rotate.  The  magnet,  to  the  free  ends  of  which 
are  affixed  soft  iron  arc-shaped  pole  pieces,  and  the  armature  core 
with  the  sides  of  the  H  correspondingly  arc  shaped,  is  shown  in 
vertical  section  in  Fig.  13-22.  In  the  slot  formed  in  the  armature 


N 


N_ 


FIG.  13-22. 

core  by  the  sides  of  the  H,  wire  is  wound  in  turns  lengthwise  of 
the  armature  shaft.  So  much  for  the  construction  of  the  ele- 
mentary magneto.  In  order  to  understand  how  it  generates  in 
its  armature,  when  turned,  an  electric  current,  it  is  necessary  to 
remember  one  law  of  physics,  namely:  Whenever  a  wire  is  wound 
about  a  magnetized  soft  iron  core  and  the  magnetism  of  the  core 
suddenly  dies  out,  there  will  be  a  tendency  for  a  current  to  be 


418  INTERNAL  COMBUSTION  ENGINES 

produced  in  the  wire.  A  familiar  example  of  the  working  of 
this  law  is  found  in  the  operation  of  the  common  jump-spark  coil. 
Here  we  have  a  core  made  of  soft  iron  wires  and  around  it  is 
wound  a  great  many  turns  of  fine  wire,  the  ends  of  which  are  con- 
nected to  a  spark  plug.  The  core  is  also  wound  with  a  coil  of 
wire  which  is  supplied  with  current  from  a  battery,  and  when  this 
current  is  flowing  the  core  is  magnetized.  When  the  current 
from  the  battery  is  interrupted,  the  magnetism  in  the  core  sud- 
denly dies  out,  and,  in  accordance  with  the  law  above  stated,  a 
tendency  is  created  for  a  current  to  flow  in  the  fine  wire  coil  which 
is  connected  to  the  spark  plug  and  this  ' induced'  current  jumps 
at  the  plug. 

"In  order  to  explain  how  the  iron  core  of  the  magneto  arma- 
ture with  its  winding  is  magnetized  and  how  the  magnetism  of 
the  core  is  caused  suddenly  to  die  out,  it  is  necessary  to  refer  to 
four  diagrams  of  Fig.  13-22,  showing  the  armature  in  different 
positions  of  rotation  with  respect  to  the  pole  pieces.  In  diagram 
(I)  the  armature  is  represented  with  the  two  heads  of  its  core  in 
close  proximity  to  the  faces  of  the  pole  pieces.  The  space  be- 
tween the  pole  pieces  is  thus  almost  -completely  filled  or  bridged 
with  iron,  and  magnetism  passes  from  one  pole  piece  to  the  other 
through  the  armature  core,  thoroughly  magnetizing  it.  Next 
consider  diagram  (II).  Here  the  armature  is  shown  rotated  into 
such  a  position  that  one  edge  of  each  pole  of  the  armature  core  is 
just  leaving  the  vicinity  of  one  of  the  pole  pieces.  As  soon  as  this 
position  is  passed,  the  space  from  pole  piece  to  pole  piece  is  no 
longer  filled  with  iron,  but  with  air  which  is  not  a  conductor 
of  electricity.  Thus  very  little  magnetism  passes  from  one 
pole  piece  to  the  other  and  the  core  is  no  longer  traversed 
by  the  magnetic  influence  and  suddenly  ceases  to  be  mag- 
netic. This  is  exactly  the  condition  prescribed  by  the  above 
quoted  law  for  the  production  of  a  current,  and,  in  fact,  when  the 
armature  in  its  rotation  leaves  position  (II),  there  is  a  sudden 
impulse  of  current  produced  in  'the  wire  of  the  armature  which 
dies  away  after  the  armature  rotates  a  little  beyond  this  position. 
In  position  (III),  the  conditions  of  armature  magnetization  exist- 
ing in  position  (I)  are  reproduced,  except  that  the  armature  has 
changed  ends  in  respect  to  the  pole  pieces  and  the  magnetic  in- 
fluence passes  through  it  in  the  opposite  sense,  charging  it  oppo- 


GAS  ENGINE  AUXILIARIES  419 

sitely,  so  that  when  the  magnetism  is  discharged  in  position  (IV) 
the  current  will  be  in  the  opposite  direction  through  the  wire  of 
the  armature  winding.  As  the  armature  is  turned  upon  its  shaft, 
there  are  thus  produced,  in  each  complete  rotation,  two  rather 
short  impulses  of  current  of  opposite  direction  nearly  correspond- 
ing with  the  instants  at  which  the  armature  heads,  so  to  speak, 
'part  company'  with  the  pole  pieces  and  are  half  a  revolution 
apart.  During  the  remainder  of  the  rotation  there  is  no  current 
flowing.  It  may  be  readily  seen  that  by  connecting  one  end  of 
the  armature  wire  to  the  armature  core,  and  by  connecting 
the  other  to  an  insulated  metallic  contact  segment,  carried 
by  the  armature  shaft,  upon  which  bears  a  stationary  insu- 
lated brush,  the  current  impulses  may  be  taken  from  the  magneto 
for  use. 

"Now  as  to  the  practical  use  of  such  a  magneto  for  ignition 
purposes.  Since  it  is  only  during  a  small  part  of  the  armature 
rotation  that  current  is  being  generated,  it  is  necessary  to  rotate 
the  armature  shaft  at  such  a  speed  that  these  electrical  impulses 
shall  be  so  timed  as  to  correspond  with  the  periods  when  ignition 
is  required  by  some  one  cylinder  of  the  engine.  If  this  were  not 
attended  to,  the  ignition  periods  of  the  engine  might  occur 
during  the  parts  of  the  armature  revolution,  when  no  current 
was  being  produced.  In  order  to  bring  about  this  result,  the 
magneto  and  the  engine  must,  at  all  times,  run  at  a  properly 
proportioned  ratio  of  speeds  and  the  positions  of  the  engine,  crank 
shaft,  and  armature  must  be  adjusted  right  in  the  first  place.  If 
the  magneto  shaft  is  geared  to  the  engine  at  the  right  ratio  and 
the  teeth  of  the  two  gears  are  correctly  meshed,  the  desired  re- 
sult will  be  brought  about.  For  instance,  if  the  engine  be  of  the 
four-cylinder,  four-cycle  type,  four  sparks  will  be  required  for 
each  two  crank-shaft  rotations.  Four  sparks  will  be  produced 
for  each  two  revolutions  of  the  magneto,  as  well,  and  thus,  if  the 
magneto  and  the  engine  run  at  the  same  speed,  the  sparks  will  be 
numerically  correct.  If  geared  to  the  crank  shaft,  the  crank- 
shaft gear  and  the  magneto  gear  would  have  the  same  number 
of  teeth,  and  if  driven  from  a  two  to  one  shaft,  the  number 
of  teeth  in  the  two  to  one  shaft  gear  would  be  twice  as  great 
as  the  teeth  of  the  magneto  gear.  By  changing  the  particu- 
lar teeth  of  one  gear  which  are  in  mesh  with  certain  teeth 


420 


INTERNAL  COMBUSTION  ENGINES 


i  + 


of  the  other,  the  current  impulses  may  be  made  to  occur  at  the 
moments  when  the  pistons   are  exactly  in  the  firing  positions." 
+  In  variable-speed  engines,  as  automobile  ma- 

chines, for  instance,  the  service  required  of  the 
ignition  outfit  becomes  more  exacting  as  the  speed 
increases,  owing  to  greater  compression  and  less 
available  time.  This  in  the  case  of  mechanical 
current  generators  is  met  by  a  natural  increase  in 
voltage  with  increase  in  speed,  which  constitutes 
another  advantage  of  this  type  of  generator  as 
compared  with  primary  and  secondary  cells.  Thus 
less  hand  manipulation  of  the  spark  is  required, 
but  all  magneto  systems  should  be  provided  with 
means  of  altering  the  armature  position  relative 
to  the  crank -shaft  position  in  order  to  alter  the 
time  of  spark. 

METHODS  OF  CONNECTING  UP  PRIMARY  AND 
SECONDARY  BATTERIES,  AND  SYSTEMS  OF  WIRING 
USED.  —  Primary  and  secondary  cells  may  be 
connected  in  series,  in  parallel  (or  multiple)  and 
in  multiple-series.  The  meaning  of  these  terms 
is  explained  in  Fig.  13-23.  For  series  connec- 
tions, Fig.-  13-23a,  each  positive  element  of  one 
cell  is  connected  to  the  negative  element  of  the 
next,  leaving  free  the  negative  element  say  of 
the  first  cell  and  the  positive  element  of  the 
last  for  connection  to  the  outside  circuit.  In 
the  second  or  multiple  method  of  connection, 
Fig.  13-236,  all  the  like  elements  of  the  cell  are 
connected  together.  Fig.  13-23c  finally  shows  six 
VJ— /  cells  in  multiple  series,  i.e.,  three  each  are  con- 

I  nected  in  series,  and  these  two  sets  in   multiple 

I  or   parallel.     To    compute   the   voltage    and   am- 

perage that  each  one  of  these   combinations  will  furnish  to  the 
outside  circuit,  let 

N  =  number  of  cells  in  the  combination 
V  =  voltage  of  one  cell,  and 
A  =  amperage  of  one  cell. 


GAS  ENGINE  AUXILIARIES  421 

Then  the  following  formulae  will  give  the  desired  information: 


Kind  of  Combination 

Series 

Multiple 

Multiple-series 

Voltage  of  set     

NV 

V 

NV 

Amperage  of  set  

A 

NA 

2A 

The  ordinary  dry  cell,  as  stated,  furnishes  about  1.5  volts 
and  12  to  15  amperes.  A  make-and-break  circuit  should  operate 
properly  on  about  8  to  10  volts,  hence  from  5  to  7  dry  cells  in 
series  are  required  for  this  service.  As  far  as  jump-spark  systems 
are  concerned  the  following  table  gives  pressures  and  currents 
required  to  operate  some  of  the  well-known  spark  coils,  together 
with  other  interesting  information.*  From  this  table  it  is  clear 
that  from  4  to  6  dry  cells  in  series  are  sufficient  to  operate  most 
jump  spark  coils: 


Volts 

Amps. 

Vibration 
per  sec.  of  j 
Trembler 

Prim. 
Res. 
Ohms. 

Sec. 
Res. 
Ohms. 

Kingston 

89 

Apple  

5.20 

2.2 

94 

.171 

3715 

Guenet       

3.7 

1.31 

111 

.300 

2337 

Guenet 

5  8 

123 

2337 

Hardv 

3  78 

1  05 

122 

274 

2779 

Fisher 

5  8 

82 

149 

613 

2590 

Dow 

3.84 

.57 

149 

.210 

5394 

Lacoste             

3.72 

1.46 

177 

.232 

2006 

Lacoste      

5.62 

1.94 

197 

.232 

2006 

Heinze  

3.66 

1.31 

210 

.320 

1302 

Pittsfield  

228 

Induction  Coil  Co  

362 

1.55 

360 

.312 

6180 

Milwaukee  

390 

.312 

6180 

Turning  next  to  the  systems  of  wiring  used,  all  make-and-break 
systems  are  low-tension  systems,  i.e.,  the  voltage  does  not  gen- 
erally exceed  8  to  10  volts.  Fig.  13-24  f-  shows  such  a  system  in 
diagram  with  a  magneto  as  the  source  of  current.  The  circuit 
is  easy  to  trace.  One  side  of  the  electrical  conductor  on  the 
armature  is  grounded,  that  is,  connected  to  the  engine  frame 

*H.  G.  Chatain  in  the  Automobile,  July  18,  1907. 

f  The  following  three  figures  ar.e  from  an  article  by  C.  B.  Hayward  in  the 
Automobile,  April  4,  1907. 


422 


INTERNAL  COMBUSTION  ENGINES 


through  the  armature  shaft  and  the  frame  of  the  magneto  itself, 
as  shown  at  G^.     The  other  end  sends  its  current  to  one  electrode 


FIG.  13-24.  —  Simplicity  of  the  Wiring  of  Low-tension  Systems. 

of  the  make-and-break  mechanism  at  A.  When  the  commutator 
or  timer,  J5,  makes  contact,  current  flows,  the  circuit  being  com- 
pleted by  grounding  B,  as  shown  at  G2. 

Jump-spark  systems   are   called  high-tension  systems,   but  a 
distinction  should  be  made  depending  upon  whether  high  or  low 


FIG.  13—25.  — Wiring  Diagram,  " High-tension  with  Coil  System." 

tension  magnetos  are  used.  With  a  low-tension  magneto  it  be- 
comes necessary  to  use  the  ordinary  spark  coil,  and  hence  this 
method  is  sometimes  called  the  high-tension  with  coil  system. 
Fig.  13-25  shows  the  wiring  for  such  a  system,  A  being  the  con- 


GAS  ENGINE  AUXILIARIES 


423 


denser  and  B  the  primary  and  secondary  windings  of  the  spark 
coil.  It  is  comparatively  easy  to  trace  out  the  complete  primary 
and  secondary  circuits,  if  one  takes  into  account  the  proper 
ground  returns. 

The  true  high-tension  jump-spark  system  differs  from  the 
above  in  the  fact  that  the  high-tension  magneto  embodies  the 
secondary  winding  and  the  condenser  of  the  spark  coil.  Hence 
the  use  of  a  separate  spark  coil  is  avoided.  In  Fig.  13-26  the  two 
windings  are  indicated  on  the  armature,  but  the  condenser  is 
shown  at  one  side  for  the  sake  of  clearness.  This  diagram  shows 
the  wiring  for  four  plugs. 


FIG.  13-26.  —  Wiring  Diagram  of  True  High-tension  System. 

HIGH-TENSION  DISTRIBUTOR.  —  With  the  ordinary  system  of 
jump-spark  ignition,  as  many  coils  as  there  are  cylinders  are 
required.  It  is  possible,  however,  by  placing  a  distributor  in  the 
high-tension  side  to  serve  a  number  of  cylinders  from  one  spark 
coil.  The  advantage  of  such  a  system  is  obvious,  although  it  is 
bought  at  the  cost  of  placing  a  make-and-break  mechanism  under 
very  high  voltage.  The  difficulties  inherent  in  this,  however, 
have  been  fairly  successfully  overcome.  The  difference  in  the 
wiring  is  made  clear  by  Fig.  13-27  and  Fig.  13-28,*  both  applying 
to  four-cylinder  engines.  The  former  shows  the  four-part  timer 
connected  to  the  four  spark  coils  serving  the  plugs  S  P^  to  S  P4. 
In  Fig.  13-28,  a  high-tension  distributor  D  connects  the  high- 
tension  side  of  the  single  coil  first  with  one  plug,  then  with 
another  as  may  be  required.  In  practice  the  high-tension  distrib- 
*  Both  from  Hibbert,  Electric  Ignition  for  Motor  Vehicles. 


424 


INTERNAL   COMBUSTION  ENGINES 


utor  D  and  the  primary  commutator  or  timer,  C  M,  are  com- 
bined in  one  device.  Fig.  13-29  shows  the  Grouse-Hinds  Double 
Ball  Contact  distributor  and  Fig.  13-30  the  Leavitt  distributor. 


SP, 


Sfc,    SP3 


FIG.  13-27. 


From  "battery 


FIG.  13-28. 


The  essential  thing  in  high-tension  distributors  is  that  serious 
sparking  in  the  high-tension  side  must  be  avoided.  For  that 
reason,  in  most  of  the  devices  the  primary  commutator  does  not 
establish  the  current  until  the  high-tension  distributor  is  in  con- 


GAS  ENGINE  AUXILIARIES  425 

tact  with  its  proper  plug  segment  and  the  primary  current  is 
broken  before  the  contact  in  the  high-tension  side  is  over.  To 
quote  from  the  description  of  the  Grouse-Hinds  device: 

"  The  principle  is  exactly  the  same  as  that  of  the  commutator 
already  described,  Fig.  13-18.  The  distributor  has  two  cams  and 
two  sets  of  ball  contacts,  one  set  for  the  timer  and  the  other 
for  the  distributor,  the  only  difference  being  that  in  the  latter 
the  balls  in  each  contact  are  about  three-eighths  of  an  inch 
apart  and  the  cam  insulated  from  the  shaft.  The  connection  is 


FIG.  13-29.  —  Grouse-Hinds  Distributor. 

made  and  the  circuit  is  closed  for  each  cylinder  as  the  cam 
passes  between  the  balls." 

The  following  is  a  description  of  the  Leavitt  distributor  as 
given  in  a  catalogue  of  the  Uncas  Specialty  Company: 

"This  device,  two  views  of  which  are  shown  above,  consists 
of  a  cylindrical  casing,  A,  of  hard  rubber,  into  which  is  let  a  metal 
plate,  B,  at  one  end,  and  which  is  covered  by  a  hard  rubber  cap,  C, 
at  the  other  end.  Upon  a  ball  bearing  in  the  end  plate,  B,  is 
mounted  a  driving  sleeve,  D,  designed  to  be  secured  upon  an 
extension  of  the  cam  shaft,  and  carrying  fast  upon  it  contact 
blocks,  E,  E,  E,  E,  which  make  contact,  successively,  with  the 
primary  ball  contact  terminal,  F.  Thus  far  the  device  is  identical 
with  the  ordinary  timer.  The  commutator  portion  is  located 


426 


INTERNAL  COMBUSTION  ENGINES 


at  the  opposite  end  of  the  cylindrical  casing.  The  latter  is  en- 
larged at  that  end,  and  into  the  radial  wall  between  the  two 
cylindrical  portions  are  clamped  four  flat-head  studs,  G,  G,  which 
serve  as  binding  posts  for  the  spark  plug  connections.  Into  the 
end  of  the  metallic  sleeve,  D,  is  fastened  a  hard  rubber  stud,  H, 
which  at  its  outer  end  carries  a  radial  arm,  /,  which  is  of  metal 

with  a  relatively  wide  contact 
shoe  at  its  end,  which  when  the 
sleeve,  Z),  revolves,  passes  over 
the  four  contact  studs,  G,  thus 
conducting  the  current  succes- 
sively to  the  four  plugs.  The 
current  is  conducted  to  the  ro- 
tating arm  by  a  central  ball  con- 
tact, J,  secured  into  the  cap,  C. 
When  the  hard  rubber  casing  is 
moved  around  its  axis  by  means 
of  the  arm,  K,  to  vary  the  time 
of  spark,  both  primary  and 
secondary  contacts  are  equally 
displaced." 

Mufflers.  —  A  muffler  is  an 
essential  part  of  a  gas-engine 
installation  if  quiet  operation  is 
desired.  The  sudden  release  of 
a  body  of  gas  at  a  pressure  nor- 
mally of  40  pounds  per  square 
inch  above  the  atmosphere 
causes  a  sharp  noise  very  annoy- 
ing in  the  long  run.  A  muffler 
is  merely  an  enlargement  in  the 
exhaust  pipe  to  allow  of  gradual  expansion  of  the  escaping 
gases.  Many  different  schemes  are  used.  Thus  in  some  cases 
the  muffler  is  merely  a  cast-iron  pot  or  vessel  of  suitable  vol- 
ume, in  other  cases  the  muffler  is  of  more  elaborate  construc- 
tion consisting  of  a  vessel  filled  with  baffles  or  partitions  in 
various  ways  and  intended  to  expand  the  gas  gradually  and  to 
break  up  the  sound  waves.  Besides  efficiency  as  a  dampener  of 
noise  there  are  two  other  points  that  should  be  kept  in  mind 


FIG.  13-30.  —  Leavitt  Distributor. 


GAS  ENGINE  AUXILIARIES  427 

with  regard  to  mufflers,  absence  of  any  serious  back  pressure 
and  durability. 

The  increase  in  back  pressure  caused  by  a  muffler  depends 
upon  the  volume  of  the  muffler  and  upon  the  amount  of  choking 
caused  by  the  baffles.  The  minimum  volume  of  the  muffler 
should  be  at  least  five  times  the  cylinder  volume,  but  for  com- 
plete silencing  twice  this  volume  is  none  too  much.  Outside  of 
the  plain  cast-iron  muffler  pot,  it  is  probably  safe  to  say  that 
nearly  all  baffled  mufflers  increase  the  back  pressure  somewhat. 
This  fact  is  conceded  by  most  manufacturers  in  that  they  furnish 
a  cut-out  which  is  called  into  service  when  the  engine  is  to  be 
called  upon  for  a  hard  pull.  At  least  one  manufacturer,  however, 
claims  the  production  of  a  slight  vacuum  between  muffler  and 
engine  due  to  the  ejector  action  of  the  muffler. 

There  is  little  doubt  that  cast  iron  is  the  best  material  to  use 
for  mufflers,  as  it  is  least  attacked  both  by  heat  and  the  action 
of  gases.  This  is  especially  true  if  a  spray  is  used  in  the  exhaust 
pipe  for  the  purpose  of  cooling  and  condensing  the  exhaust  gas. 
Many  mufflers,  however,  for  the  sake  of  lightness  and  ease  of 
manufacture,  are  made  of  galvanized  sheet  steel  and  give  quite 
satisfactory  service. 

The  noise  of  the  air  rushing  into  the  inlet  pipes  of  an  engine 
is  also  sometimes  very  annoying  and  in  some  cases  may  cause 
undesirable  vibrations  of  doors  and  windows,  and  even  walls, 
of  the  building.  In  such  a  case  it  is  usual  to  muffle  also  the  inlet 
pipes,  and  one  of  the  best  ways  to  do  this  in  small  and  medium 
sized  engines  is  to  take  the  air  from  the  hollow  sub-base. 

In  some  yery  large  engines  the  proper  silencing  of  the  intake 
and  the  exhaust  becomes  quite  a  serious  problem,  as  the  ordi- 
nary muffler  would  become  very  large.  The  expedient  sometimes 
used  is  to  draw  the  air  through  an  underground  masonry  duct 
of  ample  size  leading  in  from  the  outside  of  the  building,  and  to 
discharge  through  a  similar  duct  into  a  chamber  from  which  the 
gases  finally  escape.  A  spray  of  water  into  the  exhaust  pipe  of 
such  engines,  close  to  the  exhaust  valve,  helps  materially. 

Figures  13-31  and  13-32  *  show  two  types  of  muffler  some- 
times used.  In  the  first  the  stream  of  gas  is  merely  divided,  in 
the  second  each  division  is  furnished  with  an  enlargement  de- 
*  Mathot,  Engineering  Magazine,  July,  1907. 


428 


INTERNAL  COMBUSTION  ENGINES 


FIG.  13-31. 


signed  to  decrease  the  gas  velocity  still  further.  Fig.  13-33 
shows  the  Powell  muffler.  The  partial  section  shows  how  the 
gas  is  broken  up  into  many  fine  streams  by 
passing  it  through  perforated  plates.  In  the 
so-called  ejector  muffler,  Figs.  13-34  and 
13-35,  made  by  the  Motor  &  Mfg.  Works 
of  Geneva,  N.  Y.,  a  part  of  the  gas  passes 
straight  out  through  a  central  pipe.  The  rest 
is  made  to  pass  a  series  of  perforated  cones 
as  shown.  It  is  claimed  that  the  central 
pipe  acts  as  an  ejector  serving  to  draw  the 
gas  through  the  cones,  thus  eliminating  back 
pressure  and  even  creating  a  vacuum  ahead 
of  the  muffler. 

Starting  Apparatus.  —  The  best  way  of 
starting  small  engines,  up  to  say  10  to  12 
horse-power,  is  to  turn  the  fly-wheel  over 
by  hand  either  in  the  direction  of  normal  rotation  until  the 
engine  picks  up,  or,  after  a  charge  has  been  drawn  in,  by  turn- 
ing it  in  the  opposite  direction 
against  the  compression  and  then 
snapping  the  spark  by  hand.  In 
starting  an  engine  in  this  way, 
it  is  essential  to  make  sure  first 
that  the  time  of  sparking  is 
rather  late,  otherwise  the  engine 
may  "buck,"  which  may  pos- 
sibly lead  to  an  accident  to  the 
person  starting  it. 

As  the  size  of  the  engine 
increases,  however,  the  manual 
labor  involved  in  the  above 
scheme  soon  becomes  too  great 
and  other  means  had  to  be  devel- 
oped. These  may  be  grouped 
under  several  heads.  It  should 
be  noted  that  none  of  these  are  quite  able  to  start  an  engine 
under  load. 

(a)  Starting  crank. 


FIG.  13-32. 


ENGINE  AUXILIARIES 


429 


(6) 


(d) 


Starting  by  smaller  engine  or  other  source  of  power. 
Starting  by  mixture. 


Starting  by  compressed  air. 

(e)  Electrical  starters. 

Of  the  methods  above  mentioned,  (a)  is  nearly  universally 
used  for  engines  up  to  15  to  20  horse-power;  beyond  this,  starting 
by  compressed  air,  method  (d),  is  generally  employed. 


FIG.  13-33.  —  Powell  Muffler. 


FIG.  13-34.  —  Ejector  Muffler. 


FIG.  13-35.  —  Ejector  Muffler. 

(a)  Most  starting  cranks  are  so  arranged  that,  when  turned 
in  the  direction  of  rotation  of  the  engine,  they  grip  the  shaft.  As 
soon  as  the  first  explosions  accelerate  the  shaft  so  that  it  turns 
faster  than  the  crank  is  being  turned,  the  latter  is  released.  This 
scheme  does  not  prevent  the  crank  from  "kicking"  back  into  the 
starter's  hand  if  the  spark  should  happen  to  be  early,  and  many 
accidents  have  resulted  therefrom.  A  crank  which  avoids  this 
drawback  is  shown  in  Fig.  13-36.  The  following  description  of 
this  device  is  from  the  Horseless  Age,  March  7,  1906: 


430 


INTERNAL  COMBUSTION  ENGINES 


"A  bushing  A,  having  a  thread  of  exceedingly  high  pitch  cut 
on  its  interior  surface,  contains  a  threaded  sleeve  B  which  serves 
as  bearing  for  the  shaft  of  the  starting  crank  C.  Rigidly  secured 
to  the  shaft  of  the  crank  C  are  a  ratchet  wheel  D  and  a  ratchet 
cam  E,  the  latter  adapted  to  engage  with  the  ratchet  E'  on  the 
motor  shaft.  In  an  extension  of  the  sleeve  B  are  a  set  of  spring 

press  pawls  F  which  are 
adapted  to  engage  with 
the  ratchet  wheel  D. 

"  The  device  is  mounted 
at  such  a  distance  from 
the  end  of  the  crank  shaft 
that  the  ratchet  cams  E 
and  E'  cannot  engage  un- 
less the  sleeve  B  is  screwed 
to  the  limit  of  its  motion 
into  the  bushing  A  by 
means  of  the  hand  wheel 
G.  In  starting  the  motor, 
the  device  being  in  the 
position  shown  in  the  as- 
sembly view,  the  action  is 
the  same  as  that  of  an 
ordinary  starting  crank. 
When  the  motor  runs  up 
to  speed,  owing  to  the 
pressure  between  the  cam 
surfaces  of  ratchet  cams 
E  and  E',  the  starting 
spindle  is  forced  back  into 

the  sleeve  B,  and  the  ratchet  cams  E  and  E'  are  thereby  dis- 
engaged. However,  if  the  motor  should  kick  back,  the  pawls 
F  would  engage  into  the  notches  in  the  ratchet  wheel  D,  and  the 
sleeve  B  would  be  rotated  and  draw  the  ratchet  cams  E  and  E' 
out  of  mesh.  The  pitch  of  the  thread  on  the  sleeve  B  is  so 
steep  that  a  very  slight  rotation  of  the  sleeve  in  the  bushing 
will  carry  it  back  far  enough  to  pull  the  starting  spindle  out 
of  engagement  with  the  crank  shaft.  The  pawl  and  ratchet 
mechanism  is  completely  enclosed  by  a  lateral  extension  on 


rHE   HORSELESS  AGE 


FIG.  13-36.  —  Starting  Crank. 


GAS  ENGINE  AUXILIARIES  431 

the  bushing  A  and  an  end  plate  bolted  to  the  extension  of  the 
sleeve  B." 

(b)  If  the  plant  has  other  engines  in  operation  or  if  there  is  a 
shaft  in  operation  it  is  quite  easy  to  transmit  the  motion  to  the 
engine    to    be    started.     Some    large    engine    installations    were 
equipped  with  smaller  engines  the  shaft  of  which  carried  a  pinion 
which  meshed  with  a  ring  of  teeth  on  the  fly-wheel  of  the  large 
machine.     When  the  large  engine  picked  up  its  cycle,  the  small 
engine  was  automatically  put  out  of  mesh  with  the  wheel.     The 
cost  of  fitting  a  large  engine  for  starting  in  this  matter,  however, 
is   considerable.     Hence  this  method  has  been  largely  replaced 
by  the  use  of  compressed  air. 

(c)  Starting  by  means  of  the  fuel  mixture  is  done  in  various 
ways.     The  scheme  appears  to  be  reliable  in  the  case  of  engines 
using  illuminating  gas;  for  other  gases  it  never  was  in  any  ex- 
tended use  and  in  fact  is  to-day  nearly  obsolete.     Besides  the  fact 
that  if  the  first  charge  should  fail  there  was  generally  not  enough 
left  for  a  second  trial,  the  storing  of  an  explosive   mixture   is 
obviously  attended  with  some  danger. 

In  nearly  all  cases  of  starting  by  the  fuel  mixture,  the  engine 
crank  is  put  a  few  degrees  above  center,  i.e.,  well  in  the  beginning 
of  the  expansion  stroke:  One  method  is  to  charge  the  com- 
pression space  with  air  at  atmosphere  pressure,  and  then  to  open 
the  gas  cock.  The  mixture  formed  is  allowed  to  escape  through 
a  special  check  valve  and  is  ignited  by  a  Bunsen  burner  just  at 
the  orifice.  When  the  issuing  flame  burns  reddish,  showing  that 
the  mixture  is  rich,  the  gas  valve  leading  into  the  cylinder  is 
suddenly  closed  off.  The  flame  at  the  orifice  of  the  check  valve 
strikes  back  into  the  combustion  chamber  and  explodes  the 
mixture  remaining.  The  pressure  generated  closes  the  check 
valve  and  drives  the  piston  forward.  This  is  the  original  method 
of  Clerk  and  of  Green. 

The  pressure  generated  behind  the  piston  in  the  above  manner 
is  not  very  high,  and  the  velocity  attained  therefore  correspond- 
ingly low.  The  next  step  in  the  development  was  then  to  com- 
press the  charge  before  ignition.  The  Clerk  pressure  starter  and 
the  Clerk-Lanchester  high-pressure  starter  are  of  this  type.  Fig. 
13-37  *  shows  the  latter  gear.  The  method  of  operation  is  as 
*  Clerk,  The  Gas  and  Oil  Engine. 


432 


INTERNAL  COMBUSTION  ENGINES 


follows:  As  the  engine  is  slowing  down  for  a  stop  with  the  main 
gas  valve  closed  off,  valve  W  is  opened.  This  draws  fresh  air 
into  the  chamber  D  and  the  pipe  D'  through  the  valve  Y.  When 
next  the  engine  is  to  be  started,  the  gas  cock  F  is  opened.  Gas 
flows  into  D  and  D'  and  forms  a  combustible  mixture.  Through 
a  cock  on  the  cylinder,  or  a  slightly  open  exhaust  valve,  a  part 
of  the  mixture  is  allowed  to  fill  the  combustion  chamber  through 
the  valve  W,  while  another  part  escapes  through  a  check  valve  Y 
and  is  ignited  by  the  Bunsen  burner  X.  As  soon  as  the  mixture 
is  right,  F  is  closed  off,  the  flow  stops,  and  the  flame  strikes  in 
through  Y  into  D.  The  pressure  generated  closes  Y.  The  flame 


FIG.  13-37.  —  Clerk-Lanchester  Starter. 

and  pressure  wave  travels  around  into  Df,  compressing  the  still 
unburned  charge  ahead  of  it  and  finally  ignites  the  charge  so 
compressed  in  the  combustion  chamber  A.  The  starting  pressure 
so  obtained  is  about  twice  that  obtained  by  the  method  first 
described. 

Besides  these  flame  starters,  of  which  there  are  a  number  of 
modifications,  other  methods  are  in  use.  Thus  in  some  engines 
a  mixture  is  pumped  under  more  or  less  pressure  by  hand  into  the 
combustion  chamber,  and  ignited  either  by  snapping  the  spark, 
or,  as  it  is  done  by  one  manufacturer,  by  suddenly  lighting  an 
ordinary  parlor  match,  the  head  of  which  is  allowed  to  slightly 
project  into  the  mixture.  The  device  for  doing  this  is  quite 
simple  but  the  method  is  not  much  used. 

Another  scheme  is  to  charge  a  pressure  tank  with  the  combus- 


GAS  ENGINE  AUXILIARIES  433 

tible  mixture.  This  is  generally  done  by  means  of  a  special  valve 
which,  when  the  engine  is  in  operation,  opens  somewhere  along 
the  compression  stroke  of  the  engine,  and  allows  it  to  compress 
some  of  its  charge  into  the  tank.  The  starting  is  then  done  either 
by  merely  filling  the  combustion  chamber  under  low  pressure 
from  the  tank  and  igniting  the  mixture  by  suitable  means,  or  by 
opening  the  tank  valve  wide,  utilizing  the  pressure  of  the  com- 
pressed mixture  to  start  the  engine,  igniting  the  charge  on  the 
next  compression  stroke  in  the  regular  way.  This  scheme  has 
the  advantage  that  if  the  first  trial  fails  there  is  generally  enough 
in  the  tank  for  several  more  attempts,  but  the  storing  of  any  con- 
siderable quantity  of  mixture  under  pressure  is  not  to  be  recom- 
mended on  account  of  danger  of  explosions  in  the  tank. 

Finally,  at  least  one  large  German  engine  has  been  started  by 
means  of  the  mixture  by  first  placing  the  crank  in  the  proper 
position,  and  then  blocking  the  fly-wheel  by  a  plug  of  suitable 
material.  A  small  gas  engine  is  then  started  by  hand  and  allowed 
to  fill  the  combustion  chamber  of  the  larger  engine  under  pressure 
in  the  same  way  as  the  tank  was  charged  in  the  previous  method. 
When  the  desired  pressure  is  reached,  the  mixture  is  fired  by  hand 
manipulation  of  the  spark,  the  impulse  of  the  explosion  breaks 
the  plug  holding  the  wheel  and  the  engine  picks  up  the  cycle  in 
the  regular  way. 

(d)  To-day  the  starting  of  internal  combustion  engines  of  any 
size  is  generally  done  by  compressed  air.  The  latter  may  be 
obtained  in  various  ways.  In  some  of  the  smaller  engines,  when 
the  engine  is  to  be  shut  down,  the  fuel  valve  is  closed  and  the 
engine  as  it  slows  down  is  allowed  to  compress  the  air  drawn  in 
into  the  tank.  Some  other  installations  have  a  hand-operated 
air  compressor  for  charging  the  tank,  or  the  compressor  may  be 
belt-driven  from  the  engine  for  a  few  minutes.  It  is  hardly  neces- 
sary to  say  that  all  tank  and  pipe  connections  must  be  absolutely 
air  tight,  because  the  failure  of  the  air  pressure  in  a  plant  of  some 
size  would  cause  serious  delay.  For  engines  of  the  largest  ca- 
pacity, it  is  usual  to  employ  air  compressors  completely  indepen- 
dent of  the  engine,  thus  obviating  any  failure  due  to  tank  leakage. 

The  method  of  starting  by  compressed  air  is  to  set  the  engine 
beyond  the  center  and  then  to  give  an  impulse  through  the  start- 
ing valve.  In  some  engines-  this  valve  is  hand  operated,  in 


434 


INTERNAL  COMBUSTION  ENGINES 


others  it  is  operated  by  the  valve  gear.  Again  in  some,  especially 
single-cylinder,  engines  the  valve-actuating  gear  is  not  changed 
at  all,  except  perhaps  to  relieve  the  compression  somewhat,  while 
in  some  multi-cylinder  engines  the  gear  on  one  cylinder  is  changed 
to  make  this  cylinder  act  on  the  two-cycle  principle,  i.e.,  so  that 
it  can  take  an  air  impulse  every  turn,  until  the  other  cylinders 
have  started  regular  operation.  In  any  case  it  is  best  to  retard 
the  spark  somewhat  for  starting. 

The  starting  pressures  employed  vary  from  100  to  150  pounds, 


FIG.  13-38.  —  Air-starting  Apparatus. 

depending  upon  how  the  air  is  compressed.  In  general  one  or, 
at  the  most,  two  impulses  are  sufficient  to  start  a  machine. 

The  following  description  of  Fig.  13-38,  given  by  F.  E.  Junge 
in  Power,  April,  1906,  shows  the  method  of  starting  a  large  engine 
by  compressed  air: 

"  In  this  diagram  A  is  the  valve  controlling  the  flow  of  air 
from  a  separately  driven  air  compressor  to  the  tank  and  B  a 
similar  valve  in  the  pipe  connecting  the  tank  to  the  engine.  Both 
valves  are  mounted  on  one  pillar,  which  also  has  screwed  on  top 
of  it  a  gage  indicating  continuously  the  pressure  in  the  tank. 
Regulation  of  the  supply  of  compressed  air  to  the  engine  cylinder 
is  effected  by  means  of  an  automatic  spring-loaded  inlet  poppet 


GAS  ENGINE  AUXILIARIES  435 

valve,  the  stem  and  disc  of  which  may  be  released  or  held  fast 
by  screwing  down  or  unscrewing  the  hand  wheel  C  at  the  engine 
end  of  the  air  pipe.  A  plug  valve  D  is  inserted  in  the  air  pipe 
immediately  ahead  of  the  inlet  valve.  Before  starting  the  engine, 
the  fly-wheel  is  turned  into  such  a  position  that  the  crank  is  about 
30  degrees  above  the  inner  dead  center.  The  starting  gear  is 
adjusted  so  as  to  open  both  the  inlet  and  the  exhaust  valves  at 
the  proper  moments,  the  action  being  such  as  to  allow  part  of  the 
compressed  air  to  escape  during  a  fraction  of  the  return  travel  of 
the  piston  and  thereby  reduce  the  compression  to  about  28  pounds 
per  square  inch  for  rich  gases,  and  about  50  pounds  per  square 
inch  for  poor  gases.  In  the  meantime,  the  electric  ignition  device 
has  been  automatically  adjusted  so  as  to  retard  ignition  for  the 
first  few  strokes.  .The  main  fuel  or  gas  valves  must,  of  course, 
also  be  set  so  as  to  produce  the  most  favorable  mixture  for  starting 
conditions. 

"  To  start  the  engine,  the  air  stop  valve  B  is  opened,  the  auto- 
matic inlet  valve  released  by  screwing  down  the  hand  wheel  C 
to  the  full  extent,  and  compressed  air  is  then  admitted  by  turning 
the  handle  D  90  degrees.  The  piston  will  then  begin  to  travel 
slowly  on  its  outward  stroke,  and  just  before  it  reaches  the  outer 
dead  center  the  handle  D  must  be  returned  to  its  original  position, 
shutting  off  the  air  supply.  The  first  impulse  given  to  the  fly- 
wheel by  compressed  air  will  usually  be  sufficient  to  produce 
several  revolutions  at  a  speed  of  about  one-fifth  of  the  normal, 
when  no  load  is  on.  During  the  following  (suction)  stroke  a 
mixture  of  gas  and  air  in  the  correct  proportions  is  taken  in,  and 
on  the  next  stroke  compressed  and  ignited.  If  the  right  mixture 
does  not  happen  to  be  obtained  and  ignition  fails  to  occur,  another 
compressed  air  impulse  is  given,  which  will  always  produce  the 
desired  result.  After  the  first  power  stroke  has  been  obtained 
the  air  supply  valve  B  is  closed  and  the  automatic  inlet  valve  held 
fast  by  unscrewing  the  hand  wheel  C  until  its  hub  bears  against  a 
collar  on  the  valve  stem,  whereby  the  valve  disc  is  firmly  pressed 
on  its  seat.  Then  the  starting  gear  is  pushed  back  into  the  run- 
ning position,  so  as  to  allow  the  mechanism  to  open  the  valves 
at  the  regular  intervals  only.  The  point  of  ignition  is  thereby 
automatically  advanced  and  may  now  be  adjusted  by  hand  or 
by  the  governor  of  the  engine  so  as  to  suit  the  changed  conditions. 


436 


INTERNAL  COMBUSTION  ENGINES 


When  the  main  gas  admission  valve  is  set  in  the  correct  running 
position,  all  operations  for  starting  have  been  duly  executed. 
It  may  be  added  that  it  takes  less  time  to  perform  the  complete 
cycle  of  operations  than  it  takes  to  describe  it." 

(e)  In  central  stations,  or  in  other  locations  where  electric 
current  is  available,  starting  by  electricity  is  the  simplest  and  most 

satisfactory  met  hod.  There 
are  again  several  ways  in 
which  this  may  be  done. 

If  the  engine  drives  a 
dynamo,  it  is  possible  to 
drive  this  dynamo  as  a 
motor  from  another  source 
of  current,  until  the  fly- 
wheel has  attained  suffi- 
cient velocity.  The  layout 
for  doing  this  is  not  at  all 
simple,  however,  and  must 
be  carefully  handled.  A 
storage  battery  charged 
during  the  previous  oper- 
ation may  be  used  as  a 
source  of  current  if  no  in- 
dependent source  of  cur- 
rent is  available. 
FIG.  ia-39.  —  Motor  Starter.  A  simpler  way  is  to  gear 

an  electric  motor  to  a  rack 

on  the  fly-wheel  as  shown  in  Fig.  13-39.*  When  the  engine  picks 
up  the  motor  is  automatically  thrown  out  of  gear.  This  scheme 
has  the  merit  of  great  simplicity,  absolutely  no  change  in  the 
valve  operation  of  the  engine  being  required  for  starting. 

One  method  of  automatically  disengaging  the  motor  is  de- 
scribed in  the  Zeitschrift  d.  V.  d.  I.,  January  5,  1900.  A  general 
view  of  the  Felten  and  Guilleaume  electric  starter  for  large  en- 
gines is  shown  in  Fig.  13-40,  while  Fig.  13-41  shows  the  diagram 
of  connections  and  the  method  of  operation  for  smaller  sizes. 
The  motor  e  by  means  of  a  chain  drive  operates  the  pulley  s2. 
Rigidly  fastened  to  this  pulley  is  the  gear  22.  This  gear  in  turn 
*  F.  E.  Junge,  Power,  April,  1906. 


GAS  ENGINE  AUXILIARIES 


437 


FIG.    13-40.  —  Felten   &  Guilleaume  Electric  Starter. 

drives  a  gear  z3  which  is  pivoted  on  a  swinging  lever  ht  as  shown. 

The  arc  z  represents  the  pitch  circle  of  the  annular  gear  inside  of 

the  fly-wheel.  Arrows  indicate  the 
direction  of  operation  for  each  gear. 
One  end  of  the  lever  h±  is  connected 
by  means  of  a  strong  helical  spring  / 
to  the  toothed  segment  m.  Meshed 
with  this  segment  is  the  gear  zl 
which  is  turned  in  one  direction  or 
the  other  by  the  lever  h2,  which  is 
the  operating  handle  of  the  motor 
starting  box  a.  In  the  diagram, 
lever  h2  has  been  pulled  to  the  right 
as  far  as  it  will  go.  This  action  has 
started  the  motor  e,  and,  by  shoving 
the  segment  m  to  the  left,  has  put 
the  spring  under  considerable  tension. 
This  pulls  the  lower  end  of  h^  to  the 
right  and  causes  z3  to  mesh  with 
the  fly-wheel  z.  The  gear  23,  being 
positively  driven  from  22,  starts 
the  fly-wheel  revolving.  The  entire 
FIG.  13-41.  mechanism  is  held  in  the  position 


438  INTERNAL  COMBUSTION  ENGINES 

shown  by  a  latch  k  at  the  end  of  the  segment  m.  If  now  the 
engine  picks  up  its  cycle,  and  the  wheel  z  attains  a  greater 
velocity  than  it  can  receive  from  z3,  the  lever  h^  by  the  action 
of  the  fly-wheel  will  be  pushed  toward  the  left,  putting  the 
spring  /  under  higher  tension.  This  motion  proceeds  until  the 
upper  end  of  h^  comes  in  contact  with  and  unlatches  k,  when, 
under  the  influence  of  the  spring,  the  segment  m  is  pulled  to 
the  right  very  suddenly  and  the  motor  is  shut  off.  At  the  same 
time  the  action  of  the  fly-wheel  upon  z3  throws  this  out  of  mesh 
with  z.  The  entire  labor  connected  with  this  starter  therefore 
consists  of  the  attendants  turning  the  handle  h2  of  the  starting 
box  to  the  right  to  start  the  motor.  Beyond  this  no  further 
attention  is  required,  the  action  being  entirely  automatic. 


CHAPTER  XIV 

REGULATION    OF    GAS    ENGINES 

IN  gas  as  in  steam  engines  there  are  two  kinds  of  speed  vari- 
ation. The  first  of  these  is  directly  due  to  the  impulse  of  the 
explosion,  and  it  manifests  itself  in  a  variation  of  the  velocity  of 
the  crank  pin  during  one  engine  cycle.  To  confine  this  speed 
variation  to  within  the  allowable  limits  set  by  the  particular 
service  to  which  the  engine  is  to  be  put  is  the  function  of  the 
fly-wheel.  Fly-wheel  computations  are  beyond  the  scope  of  this 
work,  but  it  will  be  of  interest  to  point  out  briefly  the  relation 
between  the  various  types  and  combinations  of  engines  as  regards 
the  fly-wheel  weight  required  for  any  given  service.  This  weight 
depends  not  only  upon  the  closeness  of  regulation  desired,  but 
largely  also  upon  the  variation  of  the  crank  effort  during  one  cycle 
or  revolution,  and  this  in  turn  depends  upon  the  cycle  employed 
and  the  cylinder  combination. 

The  most  complete  exposition*  of  this  subject  relating  to  gas 
engines  is  given  by  Giildner,*  and  from  the  data  given  by  him  the 
following  table  (see  page  440)  is  adapted. 

In  deriving  these  figures  it  is  assumed  that  the  same  coeffi- 
cient of  fly-wheel  regulation,  designated  by  8W,  is  maintained  in 
all  cases.  This  coefficient 

o     _  y  max       V min 
°w~  y 

where  V  is  the  mean  velocity  of  the  crank  pin. 

The  second  kind  of  speed  variation  above  mentioned  is  the 
change  in  the  number  of  revolutions  of  an  engine  in  any  given 
time  due  to  a  change  of  load.  This  variation  is  taken  care 
of  by  the  governor.  Just  as  a  limit  is  set  to  the  speed 
variation  during  one  cycle,  so  an  allowable  limit  is  set  to  the  vari- 

*  Entwerfen  und  Berechnen  der  Verbrennungs-motoren,  2d  ed. 

439 


440 


INTERNAL  COMBUSTION  ENGINES 


TABLE  OF  RELATIVE  FLY-WHEEL  WEIGHTS  FOR  THE  SAME  COEFFICIENT  OF 
REGULATION;  FOR  VARIOUS  TYPES  OF  ENGINES  AND  CYLINDER  COMBI- 
NATIONS.   WEIGHT  OF  THE  FLY-WHEEL  OF  A  SINGLE-ACTING, 
SINGLE-CYLINDER,  4-CYCLE  ENGINE  is  TAKEN  =  1.00. 


Type  of  Engine  and  Cyl- 
inder Combination 

Crank  Travel 
Between  Ex- 
plosions, 
Degrees 

Relative  Fly-Wheel  Weight  for 

Equal  Cyl.  Di- 
ameter, Stroke, 
and  Revolution 

Equal  Maximum 
Horse-power 

4-Cycle 

2-Cycle 

4-Cycle 

2-Cycle 

4-Cycle 

2-Cycle 

I.  Single-Acting,   Sin- 
gle Cylinder  
II.  Double-  Acting,  Sin- 
gle Cylinder  
III.  2-Cylinder  Tandem 
Single  -Acting,     1 
Crank     

720 
540  & 
180 

360 

540  & 
180 

360 

540  & 
180 

240 
180 

360 

180 

360 

180 
360 

180 
120 

1.000 
1.230 

.796 
1.290 
.792 

1.290 

.678 

.335 

.802 
.424 

1.595 
.335 
1  .602 

.335 
.237 

1  .000 
.615 

.398 
.645 
.396 

.645 
.226 

.084 

.401 
.106 

.399 
.084 
.401 

.0.84 
.0395 

IV  .  2-Cy  Under  opposed  , 
Single-  Act  ing,       1 
Crank  

V.2  Cylinders  in  Par- 
allel, Single-Acting 
2  Cranks  together 
VI.  2  Cylinders  in  Par- 
allel,    Single-Act- 
ing,  2  Cranks,  180° 
apart    

VII.  3  Cylinders  in  Par- 
allel,   Single-Act- 
ing^ Cranks,  120° 
apart 

VIII.  4  Cylinders  in  Par- 
allel,   Single-Act- 
ing,  4  Cranks,  Nos. 
1    &    3    together, 
Nos.  2  &  4  togeth- 
er, and  180°  from 
Nos.  1  &  3  

ation  that  may  occur  in  the  number  of  revolutions  from  full  load 
to  no  load,  and  the  governor  must  be  designed  and  set  accord- 
ingly The  allowable  variation,  the  so-called  coefficient  of  gov- 
ernor regulation,  may  be  expressed  by  8r  = 


—  n. 


is    the    mean    number    of   revolutions 


where  n 


What 


REGULATION    OF   GAS   ENGINES  441 

the  values  of  8W  or  8r  may  be  depends  altogether  upon  the  kind 
of  service,  and  the  value  of  8r  at  least  is,  or  should  be,  clearly 
stated  in  all  engine  specifications.  The  value  of  Sw,  that  is,  the 
variation  in  the  angular  velocity  of  the  engine,  can  be  made  any- 
thing, depending  upon  the  weight  of  the  wheel  put  in.  It  usu- 
ally varies  from  8W  =  ¥V,  for  ordinary  commerical  service,  to  8W=  ?%* 
say,  for  the  most  exacting  service  required  for  the  operation  of 
alternating-current  generators  in  parallel.  The  value  of  the  co- 
efficient of  governor  regulation  8r  usually  varies  between  £$  and 
2^7  i-6-,  the  speed  variation  is  from  2  to  4  per  cent. 

The  theory  of  centrifugal  governor  design  as  applied  to  gas 
engines  governing  by  throttling  or  cut-off  cannot  be  taken  up 
here,  except  merely  to  state  that  it  is  best,  especially  in  the  case 
of  the  power  gases,  to  have  the  governor  act  upon  the  mechanism 
that  positively  operates  the  admission  gear  rather  than  upon  the 
admission  gear  direct.  In  this  way  the  governor  does  not  in  gen- 
eral have  to  be  so  powerful  and  above  all  it  is  unaffected  by  any 
clogging  of  the  admission  gear  or  valves  due  to  tar  and  other  in- 
crustations. It  should  further  be  noted  that  any  governor  of 
this  type  that  is  too  sensitive  may  react  with  the  speed  variation 
within  one  revolution  and  will  thus  be  hunting  constantly.  Dash 
pots  only  forcibly  overcome  these  conditions,  and  it  is  better  to 
design  these  governors  with  plenty  of  adjustment  regarding  their 
sensitiveness. 

The  design  of  hit-and-miss  governors  (see  below)  is  in  general 
very  simple.  In  contradistinction  to  the  type  of  governors  above 
mentioned,  they  can  hardly  be  made  too  sensitive  or  astatic 
for  the  quicker  they  act,  the  better. 

In  the  following  we  take  up,  first,  Systems  of  Governing,  and, 
second,  Mechanical  Details  of  Governors. 

i.  Systems  of  Governing.  —  At  the  outset  an  essential 
difference  between  steam  and  gas  engines  in  the  matter  of  gov- 
erning should  be  noted.  The  working  fluid  in  the  steam  engine  is 
a  comparatively  stable  medium,  and,  as  long  as  the  pressure 
remains  constant,  one  position  of  the  governor  mechanism 
always  corresponds  to  the  same  load,  cycle  after  cycle  recurring 
with  the  same  development  of  power.  This  is  absolutely  essen- 
tial for  close  governing,  and  in  this  respect  the  steam  engine 
has  some  advantage  over  the  gas  engine.  The  conditions  in 


442  INTERNAL  COMBUSTION  ENGINES 

the  latter  are  very  different.  The  working  fluid  is  prepared 
by  the  engine  itself,  air  and  fuel  being  mixed  at  the  engine  to 
produce  the  medium.  Various  expedients  to  this  end,  more  or 
less  successful ,  are  in  use,  but  outside  of  this,  due  to  accidents  of 
design  or  other  reasons,  stratification  of  the  charge  more  or  less 
complete,  and  variation  in  ignition,  may  result  in  unequal  veloc- 
ity of  pressure  propagation  through  the  mass  of  the  charge  giving  a 
bundle  of  different  diagrams  for  the  same  heat  value  of  the  charge. 
Thus  it  may  result  that  the  same  position  of  the  governing  mech- 
anism may  not,  and  often  does  not,  indicate  the  same  power 
developed,  and  speed  fluctuations  are  the  inevitable  result.  For- 
tunately the  mixing  and  ignition  appara£us  of  our  modern  en- 
gines can  be  made  perfect  enough  in  their  action  to  confine  these 
fluctuations  to  within  allowable  limits. 

All  gas  engine  governors  come  under  the  following  systems 
as  far  as  their  effect  upon  the  diagram  is  concerned.  Mechan- 
ically they  may  be  of  various  designs,  as  inertia,  fly-ball,  etc., 
as  shown  later: 

I.   The  Hit-and-Miss  System. 

II.  Variation  of  the  Ratio  of.  Fuel  to  Air  with  Change  in 
Load;  Quality  Governing. 

III.  Variation  of  the  Quantity  of  the  Charge  to  suit  the  Load. 
Ratio  Fuel  to  Air  remaining  constant;  Quantity  Governing. 

IV.  Combination  Systems. 

V.  Governing  by  Varying  Time  of  Ignition. 

I.    The  Hit-and-Miss  System 

This  system  effects  speed  regulation  by  cutting  out  explosions 
altogether,  depending  on  the  load.  Thus,  for  instance,  if  the 
engine  is  running  at  full  load,  the  explosions  or  cycles  will  follow 
each  other  in  regular  order  until  the  speed  has  increased  enough 
above  the  mean  to  cause  the  governor  to  act,  preventing  the  draw- 
ing in  of  the  next  charge,  thus  causing  a  "miss."  This  in  turn 
causes  the  speed  to  fall  sufficiently  below^  the  mean  to  make  the 
governor  act  the  opposite  way,  causing  the  explosions  to  recur. 
At  any  other  load  less  than  the  full  load  the  governor  action  is 
the  same,  except  that  as  we  go  down  in  the  scale  the  proportion 
of  "misses"  to  "hits"  constantly  increases.  This  system  may 
be  operated  in  any  of  the  following  ways: 


REGULATION    OF   GAS   ENGINES  443 

(a)  By  keeping  the  fuel  valve  closed,  so  that  the  engine  draws 
only  air  for  the  miss  cycle, 

(b)  By  keeping  the  inlet  valve  closed,  thus  preventing  the 
admission  of  both  fuel  and  air. 

(c)  By  keeping  the  exhaust   valve  open.     In  this  case  the 
admission  valve  is  usually  automatic,  and  its  opening  is  prevented 
by  the  fact  that  on  the  next  stroke  no  vacuum  is  formed,  the 
exhaust  gases  being  sucked  back  into  the  cylinder. 

Theoretically  this  system  of  regulation  is  the  simplest,  and, 
from  the  standpoint  of  fuel  consumption,  the  most  economical; 
practically,  however,  it  is  beset  with  certain  difficulties.  In 
theory  the  cycles  are  all  gone  through  under  exactly  the  same 
conditions,  and  hence  ratio  of  fuel  to  air,  pressure  of  compres- 
sion and  point  of  ignition  can  all  be  adjusted  once  for  all  to  suit 
the  requirements  of  best  thermal  efficiency.  The  thermal  effi- 
ciency of  the  cylinder  should  therefore  be  the  same  at  all  loads. 

In  practice  there  is  some  deviation  from  this  ideal  condition, 
even  assuming  perfect  governor  action,  but  the  variation  depends 
somewhat  upon  the  manner  of  governing.  Thus  in  engines  in 
which  only  the  fuel  valve  is  kept  closed  to  produce  the  miss  cycles, 
it  will  generally  be  found  that  the  card  directly  following  a  miss 
period  is  larger  than  those  following  it,  at  least  for  loads  approach- 
ing full  load.  This  is  due  to  the  fact  that  during  the  miss  period 
the  cylinder  has  been  thoroughly  scavenged  by  air,  causing  the 
next  charge  to  be  purer  and  somewhat  larger  in  quantity  than 
the  average.  Under  very  low  loads  the  effect  is  apt  to  be  the 
opposite,  that  is,  owing  to  a  prolonged  period  of  miss  strokes  the 
cylinder  has  cooled  so  far  as  to  make  the  first  cycles  following 
somewhat  slow  burning  until  the  cylinder  heats  up  again. 

It  is  evident  that  these  variations  must  have  their  effect  upon 
cylinder  efficiency,  but  the  effect  is  perhaps  greater  with  liquid 
fuel  engines  than  with  gas  engines  proper,  because  a  cool  cylinder  is 
likely  to  condense  some  of  the  fuel  vapor,  thus  causing  a  direct  loss. 

In  engines  that  govern  by  keeping  the  exhaust  valve  open, 
drawing  the  exhaust  gases  back  into  the  cylinder,  the  effects  above 
outlined  may  be  less  marked,  but  the  method  cannot  on  that 
account  be  recommended  as  better  than  the  other,  because  the 
inevitable  mixing  of  the  exhaust  gases  with  the  incoming  charge 
has  its  own  harmful  effects-. 


444  INTERNAL  COMBUSTION  ENGINES 

In  spite  of  these  facts,  however,  the  hit-and-miss  system  of 
governing,  no  matter  how  carried  out,  usually  shows  a  somewhat 
greater  economy  of  fuel  in  practice  than  the  other  systems. 

We  next  turn  to  the  efficiency  of  this  system  as  a  speed  regu- 
lator. It  is  evident  that  the  closeness  of  regulation  in  case  cen- 
trifugal governors  are  employed  depends  altogether  upon  the 
sensitiveness  of  the  governor,  that  is,  upon  the  facility  with  which 
it  changes  from  one  position  to  the  other;  although  it  is  possible 
here  also  to  have  a  governor  too  sensitive,  resulting  in  needless 
hunting.  But  whatever  the  type  of  hit-and-miss  governor,  the 
regulation  will  be  closest  if  at  the  higher  loads  a  constant  series 
of  explosions  is  followed  by  a  single  miss  cycle,  or  if  at  the  lower 
loads  a  single  explosion  is  followed  by  a  constant  series  of  misses. 
Thus  |  load  should  be  represented  by  the  series  Ill-Ill,  etc.,  and 
£  load  by  1  -  -  1  -  -,  etc.  Any  disturbance  of  the  gover- 
nor, accidental  or  otherwise,  as  through  want  of  care,  increased 
friction,  wear,  etc.,  will  alter  this  ideal  condition  so  that  a  f  load, 
for  instance,  may  be  represented  by  the  series  111  -  11  -  111  -  11, 
etc.  But  such  variation  at  once  unfavorably  affects  the  regula- 
tion.* These  accidental  conditions  are  not  under  the  control  of 
the  designer,  and  not  always  under  the  control  of  the  operator, 
and  the  net  result  is  that  hit-and-miss  regulation,  though  econom- 
ical, is  somewhat  unreliable  and  certainly  not  as  close  as  that  ob- 
tained by  some  of  the  other  methods,  unless  a  very  heavy 
fly-wheel  is  employed. 

Hit-and-miss  governing  is  therefore  little  employed  where 
close  regulation  is  essential,  as  for  electric  current  generation. 
For  ordinary  commercial  power  operation,  where  the  regulation 
need  not  be  closer  than  say  3  to  5  per  cent.,  the  system  is  quite 
satisfactory,  although  it  is  being  slowly  replaced  even  in  this  field. 
It  should  be  remembered  in  this  connection  that,  if  the  engine  is 
belt-connected  to  the  power  consumer,  the  flexible  connection  will 
tend  to  equalize  the  speed  variations  to  a  certain  extent. 

II.     Governing  by  Varying  the  Ratio  of  Fuel  to  Air:  Quality 

Governing 

In  this  system  the  governor  is  usually  made  to  act  upon  the 
fuel  admission  valve,  so  that  as  the  load  on  the  engine  decreases 
*  See  Mollier,  Zeitschrift  d.  V.  d.  Ingeriieure,  1903,  p.  1704. 


REGULATION    OF   GAS   ENGINES 


445 


the  engine  receives  less  and  less  fuel  in  the  same  total  charge 
volume.  This  of  course  decreases  the  area  of  the  indicator  card 
developed  to  suit  the  load.  Instead  of  acting  upon  the  fuel  valve, 
this  method  of  governing  has  also  been  carried  out  by  sucking 
back  a  certain  amount  of  the  exhaust  gases,  thus  also  decreasing 
the  heat  content  of  the  charge.  Another  way  is  to  regulate  the 
air  admission  valve,  making  the  fuel  valve  automatic.  All  things 
considered,  however?  the  first  mentioned  method  is  the  best. 

Considered  from  a  thermal  standpoint  this  system  has  the 
advantage  that,  since  the  total  charge  volume  remains  practically 
the  same  for  all  loads,  the  compression  pressure  remains  constant 
throughout.  The  cards  obtained  will  therefore  be  somewhat  as 


FIG.  14-1. 


shown  in  Fig.  14-1,  in  which  the  full  line  represents  the  full  load 
diagram.  It  therefore  should  follow  on  theoretical  grounds  that 
the  thermal  efficiency  of  the  cylinder  should  be  about  the  same 
for  all  loads.  In  practice,  however,  it  has  been  clearly  shown 
that  this  system  is  inferior  at  low  loads  to  the  next  one  to  be  de- 
scribed. In  fact,  the  fuel  consumption  per  horse-power  usually 
increases  very  rapidly  as  the  load  drops.  The  reason  is  that,  as 
the  fuel-ratio  is  decreased,  the  mixture  rapidly  becomes  difficult 
to  ignite  and,  above  all,  slow  burning.  This  necessarily  increases 
the  heat  loss  to  the  jackets  and  the  ignition  difficulty  may  go  as 
far  as  to  prevent  ignition  altogether,  causing  a  direct  loss  of  fuel. 
In  most  cases  after-burning  is  clearly  recognizable  by  the  slow 
dropping  of  the  expansion  line.  Designers  have  tried  to  over- 


446  INTERNAL  COMBUSTION  ENGINES 

come  this  difficulty  by  placing  the  time  of  ignition  also  under 
control,  making  it  earlier  as  the  load  decreases.  The  scheme, 
however,  does  not  appear  to  have  been  very  successful. 

As  a  method  of  governing,  this  system  is  capable  of  giving 
close  regulation  with  the  proper  weight  of  fly-wheel.  The  very 
fact,  however,  that  the  compression  pressure  does  not  drop  in 
proportion  to  the  maximum  pressure  introduces  a  disturbing 
factor  into  the  crank  effort  diagram  which  would  tend  to  make 
the  regulation  under  this  system  less  close  at  low  loads  than  under 
System  III. 


III.     Governing  by   Varying  the  Quantity  of  Charge  of  Constant 
Composition  to  suit  the  Load:  Quantity  Governing 

Governing  by  changing  the  quantity  of  charge  to  suit  the  load 
may  be  carried  out  in  three  ways: 

(a)  The  engine  draws  a  charge  full  stroke  each  time,  but  a 
part  of  the  charge,  depending  upon  the  load,  is  forced  back  into 
the  suction  passages,  the  inlet  valve  being  under  governor  con- 
trol. 

(6)  The  incoming  charge  is  completely  cut  off  by  the  gover- 
nor at  the  proper  time,  the  charge  expanding  behind  the  piston 
for  the  rest  of  the  stroke.  This  is  known  as  the  cut-off  method. 

(c)  The  charge  is  throttled  down  throughout  the  entire  suc- 
tion stroke,  the  governor  determining  the  position  of  the  inlet 
valves.  This  is  called  the  throttling  method. 


FIG.  14-2. 


Figs.  14-2  and  14-3  show  the  differences  in  the  diagrams  ob- 
tained under  conditions  (6)  and  (c)  outlined  above. 


REGULATION    OF   GAS   ENGINES  447 

Quantity  governing  in  general  is,  on  thermal  grounds,  open  to 
the  objection  that  the  compression  pressure  decreases  with  the 
load,  and  hence  the  cylinder  efficiency  constantly  decreases,  On 
the  other  hand,  the  mixtures  remain  readily  ignitable  down  to  the 
friction  load,  with  the  result  that  quantity  governing  is  on  the 
whole  more  economical  than  quality  governing.  The  fact,  too, 
that  the  compression  pressure  decreases  with  the  maximum  pres- 
sure has  a  favorable  influence  upon  the  crank-effort  diagram,  ad- 
mitting of  close  regulation. 

As  between  methods  (6)  and  (c),  the  former  is  slightly  better 
because  less  work  is  lost  in  the  lower  loop.  Everything  consid- 
ered, where  close  regulation  is  essential,  the  cut-off  method  of 
quantity  governing  is  the  best, 


14-3. 


Regarding  the  economy  of  the  cut-off  method  as  compared 
with  the  hit-and-miss  method  of  governing,  E.  Meyer*  finds  that 
down  to  about  \  load  the  two  systems  are  about  on  a  par.  Below 
this  load  the  efficiency  of  the  cut-off  as  compared  with  the  hit- 
and-miss  method  rapidly  falls  off. 

IV.     Combination  Systems 

It  has  been  attempted  to  perfect  quantity  regulation  by  chang- 
ing the  compression  space  so  as  to  keep  the  compression  pressure 
the  same  at  all  loads.  Thermally  this  is  a  step  in  the  right  direc- 
tion, but  no  successful  machine  operating  upon  this  system  has 
yet  appeared. 

Another  combination  system  is  that  of  Letombe,  which  is  in 
successful  use.  Letombe  regulates  by  lengthening  the  time  of 
*  Zeitschrift  d.  V.'d.  Ingenieure,  April  25,  1903. 


448 


INTERNAL  COMBUSTION  ENGINES 


opening  of  the  inlet  valve  but  decreasing  the  lift  of  the  gas  valve 
as  the  load  decreases,  As  far  as  the  fuel  is  concerned,  this  is 
quantity  regulation,  but  the  longer  time  of  opening  of  the  inlet 
valve  increases  the  total  charge  volume,  which  means  that  the 
leaner  mixtures  will  be  more  highly  compressed  than  those  for 
higher  loads.  This  is  thermaUy  correct.  Another  point  is  that 
the  richer  mixtures  at  the  higher  loads,  although  less  highly  com- 
pressed, are  less  in  total  volume  than  the  leaner  mixtures.  Hence 
as  the  load  increases  the  ratio  of  expansion  increases  as  compared 


2Q\at 


FIG  14-4. 


to  the  ratio  of  compression,  which  tends  to  draw  down  the  ter- 
minal pressure  at  the  end  of  expansion  and  decreases  the  exhaust 
loss.  The  resulting  diagrams  are  shown  in  Fig.  14-4,  given  by 
Giildner.  The  compression  line  a-b  belongs  to  the  full  load  card, 
line  c—d  to  the  minimum  load  card.  The  latter  card  shows  suc- 
tion full  stroke  and  a  compression  pressure  of  about  190  pounds, 
the  former  shows  a  suction  volume  equivalent  to  about  55  per 
cent  stroke  and  a  compression  pressure  of  about  115  pounds. 
In  spite  of  the  thermally  excellent  features,  wrhich  gives  good 


REGULATION    OF   GAS   ENGINES  449 

regulation,  the  economy  regarding  fuel  is  no  greater  than  that 
obtained  by   a   purely   cut-off  system. 

Other  combination  systems  that  have  been  employed  are 
quantity  regulation  at  high  loads  combined  with  quality  regula- 
tion at  low  loads  or  vice  versa.  This  is  done  in  some  German 
engines.  To  compensate  for  the  slow  burning  of  the  leaner  mix- 
tures the  spark  is  advanced.  Lastly,  engines  that  govern  either 
by  quantity  or  quality  regulation  at  the  higher  loads  have  been 
governed  by  the  hit-and-miss  method  at  very  low  loads.  This  is 
done  in  the  American-Crossley  engines  and  also  by  Letombe  in 
the  system  above  described. 

V.    Governing  by  Varying  the  Time  of  Ignition 

Strictly  speaking,  the  time  of  ignition  should  be  adjusted  to 
suit  the  kind  of  charge.  That  means,  for  instance,  that  in  qual- 
ity regulation  the  spark  should  be  advanced  with  a  decrease  of 
load.  It  has  already  been  mentioned  that  this  has  been  tried 
both  by  governor  control  or  by  hand  regulation.  The  former  is 
rather  difficult  because  proper  ignition  is  subject  to  so  many 
accidental  variations,  but  hand  control  is  quite  practicable  and 
all  stationary  engines  should  therefore  be  furnished  with  adjus- 
table spark  gear. 

Automobile  engines  are  generally  governed  by  hand  regula- 
tion of  the  throttle  in  combination  with  the  spark. 

Governing  of  Two-Cycle  Engines 

Small  two-cycle  engines  are  usually  governed  by  throttling 
either  the  fuel  or  the  charge.  In  the  first  case  this  results  in  what 
is  practically  quality  regulation,  in  the  second  in  quantity  regu- 
lation, Liquid  fuel  engines  of  this  type  nearly  always  govern 
by  adjusting  the  stroke  of  the  pump  to  suit  the  load,  resulting  in 
quality  regulation.  In  the  larger  machines,  which  are  nearly  al- 
ways served  by  separate  pumps,  it  is  absolutely  essential  that 
the  cylinder  be  thoroughly  scavenged.  Hence  it  is  usual  to  first 
admit  air  alone  directly  from  the  pump  or  an  intermediate 
receiver,  and  a  little  later  the  fuel  or  the  mixture  as  the  case 
may  be,  the  point  of  admission  of  the  latter  being  under  gov- 
ernor control.  The  governor  may  act  either  on  the  inlet  valve 
or  directly  on  the  pump.  It  should  be  noted  that  if  reservoirs 


450 


INTERNAL  COMBUSTION  ENGINES 


are  used  between  pump  and  engine,  there  is  likely  to  be  a  lag  of 
several  strokes  between  the  action  of  the  governor  and  its  effect 
on  the  engine.  For  more  detailed  information  on  the  governing 
of  large  two-cycle  engines,  see  the  descriptions  at  the  end  of  this 
chapter. 

2.  Mechanical  Details  of  Governors.  —  For  hit-and-miss 
governing,  inertia  governors  of  the  so-called  pendulum  type  are 
extensively  used.  Besides  this,  centrifugal  governors  of  the  fly- 
ball  type  also  find  application.  For  the  "precision"  systems 
of  regulation,  i.e.,  quantity  and  quality  regulation,  centrifugal 
governors  of  the  fly-ball  type  are  mostly  used;  shaft  governors 
either  of  the  centrifugal  or  inertia  type  are,  however,  lately  finding 
application. 

A  «  (a)   PENDULUM  OR  INERTIA  GOVERNORS 

FOR      HlT-AND-MlSS     REGULATION.     -    -     The 

simplest  form  of  this  governor  is  shown  in 
Fig.  14-5.  The  rod  a-b  carries  the  ball  weight 
c,  and  receives  an  up-and-down  motion 
usually  from  the  lay  shaft  as  shown  by 
the  arrows.  As  the  rod  moves  down,  the 
weight  strikes  the  projection  d,  and  the 
'  pendulum  is  thrown  to  the  right  as  shown 


FIG.  14-5. 


by  the  dotted  position.  If  the  speed  is  right, 
the  pendulum  will  have  gone  back  to  its 
normal  position  by  the  time  the  point  b 
reaches  the  end  of  the  valve  stem  e,  and 
the  gas  or  inlet  valve  will  be  opened.  If 
the  speed  is  above  the  normal,  a-b  will  not 
be  back  in  its  normal  position,  and  b  will 
miss  the  valve  stem  e,  causing  a  miss- 
stroke. 

A  modification  of  this,  the  bell-crank  pendulum,  is  shown  in 
Fig.  14-6.  The  action  of  this  governor  is  clear  from  the  previous 
description. 

The  disadvantage  of  these  two  forms  may  be  said  to  be  that 
they  are  thrown  a  considerable  distance  out  of  their  normal  posi- 
tion. This  is  overcome  in  what  may  be  called  spring-loaded 
pendulum  governors,  the  fundamental  type  of  which  is  shown  in 
Fig.  14-7.  As  the  bell  crank  a  b  c  moves  downward,  the  inertia 


REGULATION    OF   GAS   ENGINES 


451 


of  the  weight,  c,  throws  the  governor  into  the  dotted  position. 
If  by  the  time  the  stem  of  the  valve,  e,  is  reached,  the  spring  has 
failed  to  pull  the  governor  back  into  its  normal  position,  the  valve 
will  not  be  opened,  causing  a  miss-stroke. 


M\\\\\\M 


FIG.  14-6. 


FIG.  14-8. 

Fig.  14-8  shows  the  simplest  kind  of  inertia  governor  for  a 
horizontal  valve  stem.  This  may  be  used  with  or  without  the 
spring.  Its  action  is  sufficiently  plain. 

There  are  many  modifications  of  these  fundamental  types.* 

*  See  Giildner,  Entwerfen  &  Berechnen  der  Verbrennungsmotoren,  p.  354. 


452  INTERNAL  COMBUSTION  ENGINES 

These  will  readily  suggest  themselves  to  suit  any  particular  case. 
The  following  are  some  examples  from  actual  practice. 

Fig.  14-9  shows  a  modification  of  the  vertical  pick  blade  gov- 
ernor that  has  been  used  on  Crossley  engines.*     The  lever,  a,  is 


Gas 


actuated  by  the  cam,  and  as  long  as  the  speed  is  normal  the  spiral 
spring  on  one  arm  of  the  bell  crank  is  strong  enough  to  make  the 


FIG.  14-10. 

weight,  6,  attain  its  normal  position  in  the  time  available.  The 
blade,  c,  then  opens  the  gas  valve.  If  the  speed  rises  above  nor- 
mal, the  inertia  of  the  weight,  6,  throws  it  down  so  far  that  it  can- 
not reach  its  normal  position  in  time  and  c  misses  the  valve  stem, 

*  Giildner,  Entwerfen  &  Berechnen  der  Verbrennungsmotoren. 


REGULATION    OF    GAS   ENGINES 


453 


The  governor  on  the  Springfield  engine,  Fig.  14-10,  is  quite 
similar  to  the  above,  except  that  the  blade  acts  horizontally.* 
In  this  case  the  bell  crank  is  carried  by  the  slide,  A,  which  is  ac- 
tuated from  S.  For  normal  speed  the  blade,  P,  is  horizontal,  and 
in  this  position  hits  the  stem  of  the  gas  valve.  For  excessive 


FIG.  14-11. 


speed,  the  spiral  spring  fails  to  bring  the  weight   W  back  into 
normal  position  in  time  and  P  misses  the  gas  valve. 

An  English  design  of  hit-and-miss  governor  not  quite  so  simple 
is  shown  in  Fig.  14-1  l.f     Here  the  inlet  valve  stem,  1,  carries  the 


FIG.  14-12. 

bracket,  2.  To  this  is  pivoted  a  blade,  4,  at  3.  For  normal  speed 
of  the  engine,  the  spring,  5,  gently  presses  the  inclined  surface,  6, 
against  the  stationary  roller,  7.  In  this  position  the  blade,  4, 
will  hit  the  lever,  8,  thus  opening  the  gas  valve,  .9.  Should  the 

*  Power  Quarterly,  Oct.  15,  1900. 
f  Clerk,  Gas  and  Oil  Engines. 


454 


INTERNAL  COMBUSTION  ENGINES 


speed,  however,  rise  above  normal,  the  upward  throw  given  to 
the  blade  due  to  the  inclined  surface,  6,  sliding  against  the  roller, 
7,  becomes  excessive,  and  blade  4  fails  to  assume  its  normal  posi- 
tion by  the  time  the  lever  8  is  reached.  The  gas  valve  then  fails 
to  open. 

An  ingenious  modification  of  the  above  types  of  hit-and-miss 
governors  used  by  Delamare*  is  shown  in  Fig.  14—12.     The  stem 

of   the   inlet  slide  valve 
carries  a  small  cylinder, 

a,  into  which  is  fitted  a 
stationary  piston,  6,  air- 
tight.   The  needle  valve, 
c,  serves    to    adjust   the 
velocity    of     air    escape 
from  behind  the  piston, 

b,  With  the  cylinder,  a, 
in  the  extreme  right-hand 
position,  air  is  admitted 
behind    b    through    the 
groove,  d.    As  a  travels 
to  the  left  at  the  proper 
speed,   the    air    is    com- 
pressed,  but   it    escapes 
through  the  needle  valve, 

c,  just    fast    enough   to 
prevent  its  pushing  out- 
ward the  plunger,  /,  in 
the   branch    cylinder,   e, 
against    the   spring.     In 

FIG.  14-13.  tnjs  position  the  blade,  g, 

hits  the  gas  valve  stem,  h.  For  an  excess  in  engine  speed,  cyl- 
inder a  travels  to  the  left  so  fast  that  the  air  cannot  escape  at 
the  proper  rate,  the  pressure  generated  forces  the  plunger,  /,  out- 
ward, and  g  misses  the  valve  stem  as  shown  in  the  dotted  position. 
(b)  CENTRIFUGAL  GOVERNORS  FOR  HIT-AND-MISS  REGULA- 
TION. —  A  hit-and-miss  governor  of  this  type  is  used  in  the 
French  engine  shown  in  Fig.  14-13. f  The  centrifugal  governor 

*  Schottler,  Die  Gasmaschine. 
f  Power  Quarterly,  Oct.  15,  1900, 


REGULATION   OF   GAS   ENGINES 


455 


in  the  fly-wheel,  when  the  speed  becomes  too  high,  actuates  the 
latching  arrangement  i-k  and  throws  the  oil  pump  serving  to 
charge  the  vaporizer  temporarily  out  of  action. 


FIG.  14-14. 


FIG.  14-15. 


The Robey governor,*  Fig.  14-14,  is  of  the  fly-ball  type;  normally 
the  roller,  a,  under  the  control  of  the  governor  travels  on  the  cam, 
b,  thus  opening  the  gas  valve  at  the  proper  time.    Under  excessive 
*  Schottler,  Die  Gasmaschine. 


456 


INTERNAL  COMBUSTION  ENGINES 


speed,  however,  the  roller  is  shoved  to  the  left  on  its  spindle  by 
the  governor  linkage,  and  misses  the  cam. 

The  Campbell  oil  engine  has  a  fly-ball  governor  which  operates 
to  keep  the  exhaust  valve  open  when  the  speed  exceeds  the  nor- 
mal, Figs.  14-15  and  14-16.*  The  rising  of  the  governor  weights, 
Fig.  14-16,  depresses  the  end,  0,  of  the  lever,  N,  thus  interposing 
the  plate,  P,  Fig.  14-15,  between  the  end  of  the  exhaust  lever,  M, 
and  the  stationary  bracket,  Q.  This  prevents  the  exhaust  valve 
from  closing  until  the  dropping  of  the  speed  causes  the  governor 


FIG.  14-16. 


to  withdraw  the  plate,  P,  when  the  exhaust  valve  is  again  regu- 
larly opened  by  the  sliding  piece,  K. 

A  shaft  governor  acting  to  hold  the  exhaust  valve  open  is 
used  on  the  Perkins  engine,  Fig.  14-17.f  The  exhaust  valve  is 
operated  by  the  lever  R,  which  in  turn  is  actuated  by  the  block 
A,  striking  the  end  block,  By  of  the  rod,  C.  As  the  speed  ex- 
ceeds the  normal,  the  governor  weights  move  toward  the  circum- 
ference of  the  wheel,  and,  through  suitable  linkage,  throw  the 
latch,  P,  into  a  recess  in  the  side  of  the  block,  B.  This  prevents 
the  rod,  C,  from  returning,  and  keeps  the  exhaust  valve  open. 

*  Clerk,  the  Oil  and  Gas  Engine, 
f  Power  Quarterly,  Oct.  15,  1900. 


REGULATION    OF    GAS   ENGINES 


457 


(c)  QUALITY  REGULATION. — The  quality  method  of  regulation, 
as  carried  out  for  gas  fuel,  is  best  exemplified  in  the  Niirnberg  en- 
gine. This  engine  has  separate  gas  and  inlet  valves.  At  all 


FIG.  14-17. 

loads  the  inlet  valve  opens  and  closes  at  the  same  time,  thus  ad- 
mitting a  constant  charge  of  volume.  But  the  gas  valve,  under 
governor  control,  opens  later  as  the  load  drops,  and  closes  about 
the  same  time  as  the  main  inlet  valve.  Thus  the  composition  or 


FIG.  14-18. 


quality  of  the  mixture  changes  with  every  load.  A  certain  dis- 
advantage of  this  method  of  proportioning  the  charge  is  that  the 
mixture  is  not  only  affected  by  the  relative  time  of  opening  of 


458 


INTERNAL  COMBUSTION  ENGINES 


the  gas  and  inlet  valves,  but  also  by  the  relative  velocities  of  the 
gas. and  air  currents.  Thus  at  low  loads,  when  the  gas  valve  opens, 
the  gas  column  has  to  start  from  rest,  while  the  air  column 
already  has  its  maximum  velocity.  The  time  needed  for  the  accel- 
eration of  the  gas  column  is  practically  constant,  hence  this  factor 
affects  the  mixture  differently  for  every  load.  Another  point 
is  that  unless  the  gas  valve  closes  quickly  there  is  apt  to  be  so 
much  throttling  of  gas  as  to  make  the  mixture  drawn  in  at  the 
end  for  low  loads  incombustible.  This  is  especially  bad  since 
this  mixture  is  apt  to  be  located  around  the  igniter. 

The  governor  used  on  the  Niirnberg  engine  is  of  the  ordinary 
fly-ball  type.  The  trip  gear  for  the  gas  valve  is  shown  in  Fig. 
14-18.*  The  governor  determines  the  position  of  the  bell-crank 


FIG.  14-19. 

lever  e-g,  and  through  this  the  position  of  the  wiper  cam  lever  d. 
The  eccentric  rod,  6,  through  the  latch  blf  lifts  the  gas  valve  by 
depressing  the  valve  lever,  a.  The  position  of  d  determines  the 
time  of  opening.  The  valve  is  closed  practically  instantaneously 
by  the  coil  spring  shown  in  the  top  of  the  housing  as  soon  as  the 
small  roller,  c,  has  released  the  latch  6X.  The  dash  pot,  /,  serves 
to  dampen  the  drop  of  the  valve,  making  it  close  without  shock. 
Many  oil  engines  are  governed  by  what  is  practically  quality 
regulation.  Thus  the  Hornsby-Akroyd  oil  engine,  Fig.  14-19, f 
takes  a  full  charge  of  air  every  stroke,  but  the  quantity  of  oil  is 

*  Power,  Feb.,  1906. 

f  Guldner,  Verbrennungsmotoren,  p.  119. 


REGULATION    OF    GAS    ENGINES 


459 


changed  to  suit  the  load.  The  quality  of  the  mixture  therefore 
changes  for  every  different  load.  The  proportioning  of  the  oil 
supply  to  the  load  is  accomplished  as  follows.  The  oil  pump 
supplies  a  constant  quantity  of  oil  every  stroke  to  the  vaporizer 
valve,  c.  This  valve,  however,  is  a  two-way  valve,  one  exit  open- 
ing through  an  atomizing  nozzle  into  the  vaporizing  chamber, 
while  the  other  allows  some  of  the  oil  to  flow  back  into  the  oil 
tank.  The  fly-ball  governor,  through  the  linkage  shown,  controls 
the  size  of  this  overflow  opening,  c',  and  thus  determines  the 
amount  of  oil  which  enters  the  vaporizer  chamber. 


FIG.  14-20. 

The  governing  mechanism  of  a  small  Diesel  oil  engine  is  shown 
in  Fig.  14-20.*  The  pump  plunger,  a,  is  actuated  by  the  lay  shaft, 
h.  The  suction  valve  is  shown  at  c  and  the  automatic  discharge 
valve  at  b.  The  oil  under  pressure  flows  through  b  to  the  atomiz- 
ing nozzle.  The  amount  of  oil  required  for  the  load  on  the  engine 
at  any  given  time  is  measured  by  controlling  the  time  of  closing 
of  the  suction  valve,  c,  forcing  more  or  less  of  the  oil  back  into  the 
*  Giildner,  Verhrennungsmotoren,  p.  379, 


460 


INTERNAL  COMBUSTION  ENGINES 


oil  supply  tank.  The  motion  of  valve  c  is  controlled  through 
linkage  not  shown,  by  the  governor  lever  e.  At  g  this  lever  re- 
ceives an  up-and-down  motion  from  the  lay  shaft,  but  the  manner 
in  which  this  motion  is  transmitted  to  the  suction  valve  depends 
upon  the  position  of  the  fulcrum,  /,  which  is  determined  by  the 
governor,  thus  varying  the  time  of  closing  of  the  valve. 

(d)  QUANTITY  REGULATION.  —  Koerting  Bros,  govern  their  four- 
cycle engine  as  follows,  Fig.  14-21*:  Air  enters  through  the  pipe, 
D,  and  gas  through  B.  The  two  are  mixed  in  the  proportion 
suited  to  the  particular  gas  by  the  mixing  valve  A.  This  valve 


FIG.  14-21. 

when  once  adjusted  therefore  furnishes  a  mixture  of  constant  qual- 
ity. To  suit  the  quantity  of  this  mixture  to  the  load,  the  gover- 
nor controls  the  position  of  the  throttle  valve  e  in  the  passage 
leading  from  the  mixing  valve  to  the  inlet  valve.  This  valve  thus 
throttles  the  charge  during  the  entire  suction  stroke. 

A  very  similar  arrangement  is  used  in  the  Westinghouse  vertical 
engine,  Fig.  14-22. f  A  is  the  throttle  valve  controlling  the  entrance 
of  the  mixture  to  the  cylinder.  Its  position  depends  upon  the 

*  Schottler,  Die  Gasmaschine. 

f  L.  S.  Marks,  Instruction  Paper  on  Gas  and  Oil  Engines. 


REGULATION    OF    GAS    ENGINES  461 

action  of  the  fly-ball  governor,  B.  Gas  enters  the  interior  of  this 
valve  through  ports  G  and  air  through  ports  D.  The  .relative 
proportions  of  these  ports  are  fixed  by  slides  H-H,  so  that  the 
proper  relation  of  air  to  gas  for  the  fuel  used  can  be  established  and 
maintained. 


FIG.  14-22. 

Fig.  14-23  shows  the  arrangements  for  operating  and  control- 
ling the  mixing  valve  in  the  Ehrhardt  and  Sehmer  engine,  which 
is  a  modification  of  the  Deutz  engine.*  It  will  be  readily  seen,  by 
a  study  of  the  figure,  that  the  governor,  through  its  linkage,  con- 
trols the  position  of  the  fulcrum,  about  which  the  valve  lever 
turns.  The  farther  this  fulcrum  moves  to  the  right,  the  greater  will 
be  the  opening  of  the  inlet-valve  and  the  greater,  consequently, 
also,  the  amount  of  mixture,  proportioned  in  passing  the  valve, 
admitted  to  the  cylinder. 

It  will  be  noted  that  all  of  the  above  examples  of  quantity 
governing  throttle  the  mixture  throughout  the  suction  stroke.  It 
was  pointed  out,  in  the  discussion  on  various  systems  of  govern- 
ing, that  the  system  employing  quantity  regulation  with  cut-off 
was  superior  to  thai  which  throttles  the  charge  throughout  the 
stroke,  and  it  seems  surprising,  therefore,  that  this  system  is  not 
in  more  extended  use.  There  is  to  the  writer's  knowledge  only 

*  K.  Reinhardt,  Bi-monthly  Bulletin  of  the  Am.  Inst.  of  Mining  Engineers, 
November,  1906,  p.  1092 


462 


INTERNAL  COMBUSTION  ENGINES 


one  engine  in  this  country  employing  the  cut-off  system,  the  Sar- 
gent complete  expansion  engine.  This  engine  employs  a  Rites 
inertia  governor  which  acts  upon  the  lay  shaft  driving  gear  which 
is  loose  on  the  crank  shaft.  As  the  load  increases  or  decreases, 
the  governor  retards  or  advances  this  gear  relative  to  the  crank 
shaft,  thus  affecting  all  of  the  valve  events  depending  upon  the 
lay  shaft  at  the  same  time.  Since  near  the  end  of  the  stroke, 
however,  the  piston  velocity  is  comparatively  small,  a  relatively 


FIG.  14-23. 

large  advance  or  retardation  of  the  gear  will  not  affect  the 
exhaust  events  or  the  beginning  of  the  suction  stroke  very 
much.  But  the  cut-off  occurs  along  the  suction  line  some- 
where near  the  time  when  the  piston  has  its  maximum  velocity, 
and  hence  a  relatively  small  advance  or  retardation  of  the  gear 
is  sufficient  to  change  the  cut-off  materially  and  hence  to 
control  the  speed. 

(e)  COMBINATION  QUANTITY    AND    QUALITY  REGULATION.  - 
The   purpose  of    these   combination  systems    has    already   been 


REGULATION    OF    GAS    ENGINES 


463 


pointed  out.  Fig.  14-24  shows  the  method  as  carried  out  by 
Reichenbach.*  The  governor,  through  the  rod,  c,  controls  the 
position  of  the  bell  crank  lever,  d.  This  lever  has  two 
slotted  arms,  a  and  6.  The  former,  by  rod  and  lever,  reg- 
ulates the  position  of  the  mixing  valve,  while  the  latter, 
by  a  similar  arrangement,  controls  the  position  of  the  throttle 
valve.  Suppose  now  that  the  sliding  blocks  a  and  b  are  in 
the  position  shown  in  the  figure.  Under  these  circum- 
stances, the  movement  of  the  throttle  valve  is  insignificant 


FIG.  14-24. 

because  b  is  so  close  to  the  center.  Hence  in  this  position  the 
engine  is  practically  governed  by  quality  regulation.  If  the  posi- 
tions of  a  and  b  were  reversed,  that  is,  b  at  the  outer  end  of  its  slot 
and  a  at  the  inner  end,  there  would  be  practically  quantity  regu- 
lation. In  actual  operation  the  positions  of  a  and  b  in  their  re- 
spective slots  are  determined  by  trial  and  depend  upon  the  gas 
used.  The  final  adjustment  is  such  that  for  the  upper  ranges  of 
load  the  quality  of  the  mixture  is  changed,  while  for  the  lower 
loads  the  throttle  valve  comes  into  action  while  the  mixture  is 
*  Power,' July,  1906. 


464 


INTERNAL  COMBUSTION  ENGINES 


held  at  practically  constant  composition.  In  addition  to  this, 
Reichenbach  also  puts  the  point  of  ignition  under  governor  con- 
trol, advancing  it  as  the  load  drops. 

Reinhardt's  method  of  governing  does  not  come  strictly  under 
any  of  the  heads  so  far  discussed.  The  inlet  valve  is  shown  in 
Fig.  14-25.*  The  valve  opens  and  closes  with  the  beginning  and 
end  of  the  suction  stroke.  Above  the  valve  there  are  arranged 
a  series  of  ports,  I  for  gas  and  II  and  III  for  air.  The  flow  of  gas 


FIG.  14-25. 

or  air  from  these  ports  into  the  valve  chamber  proper  is  controlled 
by  a  slide  guided  by  the  valve  spindle.  At  the  beginning  of  the 
suction  stroke  the  slide  only  frees  the  ports  from  chamber  III, 
and  hence  only  air  is  admitted.  'At  some  point  in  the  stroke,  how- 
ever, as  determined  by  the  governor,  the  slide  is  suddenly  released 
and  forced  down  by  springs.  This  closes  ports  III  and  opens  gas 
ports  I  and  air  ports  II.  Mixture  of  the  proper  proportion  then 
*  Reinhardt,  Bi-monthly  Bulletin,  Am.  Inst.  Mining  Engs.,  Nov.,  1906. 


REGULATION    OF    GAS    ENGINES 


465 


enters  the  cylinder  until  the  end  of  the  suction  stroke.  As  far  as 
the  admission  of  a  varying  quantity  of  constant  mixture  is  con- 
cerned, this  system  is  pure  quantity  regulation;  but  since  the 
amount  of  air  drawn  from  III  increases  as  the  load  decreases,  the 
mixture  in  the  cylinder  as  a  whole  grows  leaner  as  the  load  drops. 
It  is  claimed,  however,  that  combustion  is  good  even  under  fric- 
tion load,  because  although  the  amount  of  constant  mixture  drawn 
in  is  small,  more  or  less  stratification  of  the  charge  ensures  the 
presence  of  a  fairly  rich  mixture  around  the  igniter.  The  system 
has  the  advantage  over  pure  quantity  regulation  in  that  the  com- 
pression pressure  remains  practically  unchanged. 

In  general  principle  the  above  method  of  Reinhardt  seems  to 
be  a  modification  of  the  method  of  Mees  patented  in  1901. 


FIG.  14-26. 

Letombe,  recognizing  the  serious  effect  on  thermal  efficiency 
of  the  decrease  in  compression  which  accompanies  pure  quantity 
regulation,  goes  one  step  further  and  so  arranges  the  valves  that 
the  lean  mixtures  under  low  loads  are  more  strongly  compressed 
than  the  rich  mixtures  at  the  higher  loads.  This  is  thermally  an 
important  step  in  the  right  direction.  In  Fig.  14-26,*  a  is  the 
main  inlet  valve  operated  at  a  constant  lift  by  the  cam,  d,  through 
the  lever,  e.  Ahead  of  this  inlet  valve  are  the  air  valve,  6,  and  the 
gas  valve,  c.  Valve  b  is  operated  through  the  lever,  g,  by  the 
cam,  /.  Gas  valve  c  opens  only  when  pushed  up  by  6.  Cam  / 
is  shown  in  greater  detail  at  the  left.  It  has  a  number  of  elevat 
tions,  each  of  which  consists  of  two  steps  of  different  lengths,  as 
shown  at  1,  2,  and  3.  At  full  load  the  roller  on  the  lever,  g,  mounts 
*  Schottler,  Die  Gasmaschine. 


466 


INTERNAL  COMBUSTION  ENGINES 


the  higher  step  of  elevation,  1,  opening  both  b  and  c  wide,  and  the 
mixture,  of  constant  proportion,  enters  the  cylinder  through  a, 
which  has  been  opened  at  the  same  time.  After  awhile  the  roller 
drops  to  the  lower  step  of  elevation,  1,  air  valve,  6,  closes  partly, 
closing  gas  valve,  c,  completely.  Only  air  is  then  drawn  into  the 
cylinder  until  the  roller,  g,  drops  off  the  cam  altogether.  Now 
suppose  that  the  load  drops.  The  governor  then  pulls  over  the 
roller,  g,  until  it  comes  in  line  with  elevation  2  or  3,  as  the  case 


WATCH 


IGNITION 
MECHANISM 


'"STARTING  HANDLE 
FIG.  14-27. 


may  be.  The  time  of  opening  of  the  gas  valve,  c,  is  then  short- 
ened, because  the  higher  step  of  the  elevation  is  shorter;  but  the 
time  of  admission  of  air  alone  to  the  cylinder  is  lengthened,  be- 
cause the  lower  step  of  the  cam  is  longer  than  it  was  before. 
Hence,  although  the  mixture  is  leaner,  the  total  charge  volume  is 
greater  than  at  full  load,  and  the  leaner  mixtures  therefore  receive 
a  higher  compression.  Theoretically,  this  should  give  increased 
thermal  efficiencies  at  low  loads  as  compared  with  other  systems 


REGULATION  OF  GAS  ENGINES  467 

of  regulation.     In  practice,  however,  for  reasons  not  explained, 
there  does  not  seem  to  be  much  difference. 

(/)  GOVERNING  OF  TWO-CYCLE  ENGINES.  —  Fig.  14-27  shows  a 
type  of  two-cycle  engine,  the  Lozier,*  much  used  for  small  motor 
boat  work.  As  in  all  machines  of  this  kind,  the  mixture  is  formed 
and  compressed  in  the  crank-case,  and  flows  from  here  through  a 
communicating  passage  into  the  cylinder,  as  shown  by  the  arrows. 
Speed  is  controlled  simply  by  the  throttle  valve  in  the  passage, 
thus  controlling  the  amount  of  mixture  entering  the  cylinder. 
This  is  a  very  simple  case,  because  the  load  on  the  engine  is  prac- 
tically constant. 

In  the  new  Buckeye  two-cycle  engine,  which,  as  far  as  size  is 
concerned,  is  intermediate  between  the  small  two-cycle  gasoline 
engine  and  the  very  large  two-cycle  blast  furnace  gas  engines  of  the 
Koerting  or  Oechelhauser  type,  the  forward  end  of  the  cylinder  is 
used  as  a  mixture  pump.  Regulation  is  effected  by  means  of  the 
balanced  throttle  valve  60,  Fig.  12-31,  p.  289,  which,  under  the 
control  of  the  fly-ball  governor,  regulates  both  the  suction  to 
the  pump  and  the  delivery  from  the  pump  to  the  combustion 
chamber.  Thus  this  engine  governs  by  varying  the  quantity  of 
the  mixture;  but  since  the  cylinder  is  always  thoroughly  scav- 
enged by  fresh  air,  the  mixture  will  naturally  grow  leaner  as  the 
load  drops,  while  the  compression  pressure  remains  practically 
the  same. 

The  governing  details  of  the  Oechelhauser  two-cycle  machine 
vary  somewhat,  depending  upon  the  firm  building  them.  Fig. 
14-28  f  shows  the  scheme  adopted  by  Borsig.  It  may  be  remem- 
bered that  in  this  machine  air  and  mixture  enter  the  cylinder 
through  separate  rings  of  ports  in  the  side  of  the  cylinder,  as  soon 
as  the  piston  uncovers  them.  The  air  ports  are  uncovered  first 
to  admit  the  scavenging  air,  the  mixture  ports  a  little  later.  Each 
ring  of  ports  is  surrounded  by  a  receiver  into  which  the  air  and 
gas  pumps  deliver  their  charges  under  some  compression.  It  is 
evident  that,  since  the  time  taken  by  the  piston  to  uncover  and 
cover  the  gas  and  air  ports  is  practically  constant,  the  amount  of 
mixture  that  can  enter  the  cylinder  during  a  given  time  must  de- 
pend upon  the  pressure  in  these  receivers,  and  upon  the  port  area. 

*  Power  Quarterly,  Oct.  15,  1900. 
t  Hiedler,  Gross-Gasmaschinen,  p.  67. 


468 


INTERNAL   COMBUSTION   ENGINES 


The  governor,  therefore,  is  made  to  act  upon  the  gas  and  air  pumps 
to  control  the  pressure  in  the  receivers.  Further,  as  the  load  de- 
creases and  approaches  the  friction  load,  the  amount  of  mixture 
entering  becomes  so  small  as  compared  with  the  amount  of  air  in 
the  cylinder  that  ignition  is  likely  to  become  difficult.  For  this 
reason  the  mixture  ports  are  surrounded  by  a  slide  under  governor 
control,  as  shown  at  A,  Fig.  14-28,  which  is  operated  in  such  a 
way  that  as  the  load  decreases  the  ports  opposite  the  igniter  are 


FIG.  14-28. 

gradually  closed  first,  thus  insuring  a  comparatively  rich  mixture 
around  the  igniter  at  all  times. 

The  method  of  governing  the  Koerting  two-cycle  engine  also 
differs  somewhat,  depending  upon  the  manufacturing  firm.  In 
all  designs  there  are  a  gas  and  an  air  pump,  of  which  the  air  pump 
delivers  its  charge  into  the  cylinder  from  the  commencement  of 
its  discharging  stroke  in  order  to  scavenge  out  the  cylinder.  The 
gas  pump  runs  idle  for  a  part  of  its  discharge  stroke,  generally 
forcing  the  gas  back  into  the  suction  main,  until,  at  a  point  de- 
termined by  the  governor,  the  overflow  valve  closes,  and  the  gas 
pump  delivers  the  rest  of  its  charge  into  the  cylinder  through  a 
valve  on  top.  Fig.  14-29  *  shows  the  pump  construction  used  by 

*  F.  E.  Junge  in  Power,  November,  1906. 


470 


INTERNAL   COMBUSTION   ENGINES 


the  Gutehoffungshiitte.  Both  the  gas  and  air  pumps  are  con- 
trolled by  piston  valves  operated  by  rocker  arms  and  eccentrics. 
Situated  below  the  piston  valve  of  the  gas  pump  there  are  two 


FIG.  14-30. 

auxiliary  piston  valves,  h  and  i,  which  are  under  the  control  of 
the  governor.  Depending  on  the  load  on  the  engine,  the  gover- 
nor, through  linkage  shown  in  Fig.  14-30,  and  of  which  lever  k, 
Fig.  14-29,  is  a  part,  rotates  these  auxiliary  valves  about  their 
axis,  thus  controlling  the  time  when  the  gas  pump  commences  to 
deliver  its  charge  to  the  power  cylinder. 


CHAPTER   XV 

THE    ESTIMATION   OF    POWER    OF    GAS    ENGINES 

IT  is  intended  in  this  chapter  to  point  out  the  various  methods 
in  use  by  which  the  power  that  a  given  engine  may  be  expected 
to  develop  can  be  computed,  or,  what  amounts  to  the  same 
thing,  to  determine  the  cylinder  dimensions  for  any  given  power. 

In  steam  engine  practice  this  is  a  comparatively  simple  matter. 
It  is  necessary  merely  to  lay  down  an  ideal  indicator  card  along 
well-defined  lines,  and  then,  by  the  use  of  card  factors  closely 
fixed  by  long  practical  experience,  to  determine  the  probable 
mean  effective  pressure  in  the  cylinder  or  cylinders. 

Although  this  method  is  by  some  writers  advocated  also  for 
the  gas  engine,  the  determination  of  the  card  factor  for  gas  engines 
is  based  upon  so  many  component  factors,  which  in  turn  depend 
altogether  upon  the  judgment  of  the  designer,  that  the  result  is 
anything  but  certain.  The  difficulties  attaching  to  this  method 
are  pointed  out  in  greater  detail  below. 

Before  describing  the  various  methods  of  computing  cylinder 
dimensions  it  is  well  to  examine  briefly  into  the  allowable  piston 
speed.  The  theoretical  limit  of  piston  speed  of  course  depends 
directly  upon  the  time  of  explosion,  and  this  in  turn  depends 
upon  the  kind  of  mixture  and  to  a  certain  extent  upon  the 
method  of  ignition.  As  far  as  modern  practice  goes  the  upper 
limit  to-day  seems  to  be  at  about  800  feet  par  minute.  A  certain 
formula,  empirical  as  far  as  the  writer  is  aware,  makes  the  piston 
speed  depend  upon  the  horse-power  of  the  engine,  stating  that 

piston  speed  =  (660  +  6  \/B.  H.  P.  )  ft-  per  min.          (1) 

"  H 

in  which  B.  H.  P.n  is  the  normal  brake  horse-power. 

A  similar  empirical  formula  for  the  revolutions  per  minute 

19QQ 

13  r-p-m- = 65 + (2) 

471 


472  INTERNAL  COMBUSTION  ENGINES 

For  stationary  and  especially  low-compression  engines  the  values 
of  equations  (1)  and  (2)  should  not  be  exceeded.  For  automobile 
and  other  high-speed  work  the  revolutions  may  be  increased  up 
to  1.35  times  the  value  computed  from  equation  (2). 

I.  The  First  Method  of  Horse-power  Computation  is  more  or 
less  empirical  in  that  it  depends  either  upon  the  outright  assump- 
tion of  the  mean  effective  pressure,  or  upon  the  computation  of 
this  factor  from  empirical  or  semi-empirical  formulae.  Thus 
Grover  bases  the  determination  of  the  M.  E.  P.  upon  the  com- 
pression pressure,  making 

M.  E.  P.  =  2  C  -  .01  C2  (3) 

where  C  =  the  pressure  of  compression  in  pounds  above  atmos- 
phere. This  formula  is  derived  from  an  examination  of  a  large 
number  of  indicator  diagrams,  but  leaves  out  of  consideration 
the  kind  of  fuel  or  the  quality  of  the  mixture.  Further,  the 
formula  gives  the  maximum  result  when  the  compression  pressure 
is  100  pounds  by  gage.  Beyond  this  the  M.  E.  P.  drops.  The 
results  are  therefore  at  best  approximate  and  in  some  cases  absurd. 
S.  A.  Moss,  in  an  article  entitled  "Rational  Methods  of  Gas 
Engine  Powering/'  in  Power,  July,  1906,  goes  further  than 
Grover  and,  in  fixing  upon  the  probable  M.  E.  P.,  takes  into  ac- 
count the  size  of  engine  as  well  as  the  kind  of  fuel.  The  cooling 
loss  is  relatively  less  in  large  than  in  small  engines,  hence  the 
M.  E.  P.  may  be  expected  to  increase  somewhat  with  the  size  of 
the  engine  everything  else  remaining  the  same.  The  kind  of 
fuel  has  an  influence  upon  the  power  developed  in  any  given 
cylinder  due  to  the  fact  that  the  best  air-fuel  ratios,  i.e.,  mix- 
tures, of  the  different  fuels  have  a  different  heat  content  per 
cubic  foot.  Some  of  the  mixtures  are  poorer,  some  richer  than 
the  average;  as  computed  in  Chapter  X.  Presupposing  equal 
completeness  of  combustion,  the  richer  mixtures  yield  the  higher 
mean  pressures,  and  hence  the  greater  power.  The  following 
table  shows  the  probable  M.  E.  P.,  as  computed  by  Moss.  Only 
four-cycle  engines  are  considered  and  the  fuel  is  assumed  to  be 
average  natural  gas  or  illuminating  ~gas  (average  heat  content 
87  B.  T.  U.  per  cu.  ft.  of  mixture). 


POWER  OF  GAS  ENGINES  473 

TABLE   I.  —  VALUES   OF   MEAN   EFFECTIVE   PRESSURE   FOR   GAS   ENGINES 


X<5T 

81 

MEAN  EFFECTIVE  PRESSURES,  LBS.  PER  SQ.  INCH. 

&** 

la 

Approximate  Brake  Horse-Power  of  Engine 

III 

hi- 

5  or 
less 

10 

25 

50 

100 

200 

500 

50 

40 

60 

65 

70 

75 

60 

35 

65 

70 

75 

80 

70 

30 

70 

75 

80 

85 

85 

90 

95 

80 

28 

70 

75 

85 

90 

90 

95 

100 

90 

26 

90 

95 

95 

100 

105 

100 

24 

95 

95 

100 

100 

110 

110 

22 

95 

95 

100 

100 

110 

120 

20 

100 

100 

110 

If  some  other  kind  of  fuel  than  the  two  above  specified  is 
used,  the  M.  E.  P.  of  Table  I  should  be  multiplied  by  the  proper 
factor  from  Table  II  following: 

TABLE  II.  —  RATIOS  OF  HEAT  OF  COMBUSTION  PER  CUBIC  FOOT  OF  PERFECT 
MIXTURE,  TO  VALUE  FOR  AVERAGE  NATURAL  GAS  OR  MANUFACTURED 
ILLUMINATING  GAS  (87). 

Oil  Gas 1.00 

Water  Gas  (uncarbureted)   1.00 

Coke  Oven  Gas 93 

Air  Gas  (Siemens  Producer  Gas) 79 

Carbureted  Water  Gas    1.05 

Anthracite  Producer  Gas    «. 80 

Bituminous  Producer  Gas    87 

Blast  Furnace  Gas 67 

Acetylene  Gas 1.28 

Gasoline  (liquid,  vapor,  or  vaporized  and  mixed  with  air) 1.12 

Kerosene  (vaporized  alone  or  mixed  with  air),  and  entering  cylinder  .90 
at  about  150°  F 90 

That  the  maximum  compression  pressure  allowable  differs 
for  every  fuel  has  already  been  pointed  out  in  Chapter  IV,  where 
a  table  giving  the  compression  pressures  ordinarily  employed 
will  be  found. 

Having  thus  determined  the  probable  M.  E.  P.,  the  indicated 
horse-power  developed  at  normal  load  by  any  given  engine  may 
then  be  computed  from  the  formula 

(M.E.P.)  Ian 
33000 


I.H.P.,- 


(4) 


474  INTERNAL  COMBUSTION  ENGINES 

where      I  =  stroke  in  ft. 

a  =  piston  area  in  square  inch. 

and         n  =  no.  ot  explosions  per  minute  =  aj)out 

four-cycle  machine  at  full  load. 

It  will  generally  be  found  that  at  full  load  the  number  of 

,  .         ,  .,        i  .  .,  r.p.m. 

explosions  in  a  hit-and-miss  engine  is  not  quite  equal  to  - 

2i 

or  that  in  a  machine  governed  by  any  of  the  precision  methods 
the  card  given  at  full  load  is  not  quite  the  maximum  card  obtain- 
able. This  is  done  in  both  cases  to  give  the  engine  some  over- 
load capacity,  say  from  10  to  20  per  cent.  Assuming  an  average 
overload  capacity  of  say  15  per  cent,  we  then  have  the 

T  TT  P 
T  TT  P  i.Ji.i  -m  ,-^ 

I.H.1.,-      J15 

where      I.  H.  P.n     =  normal  or  full  load  I.  H.  P.,  and 
I.  H.  1*      =  maximum  I.  H.  P.  obtainable. 


'  m 


Now  at  full  load  the  mechanical  efficiency  of  an  average  engine 
may  be  assumed  to  be  80  per  cent,  so  that  the  normal  brake 
horse-power  will  be 

B.  H.  P.,  -.  .8  I.  H.  P.M  =  -4;  LH.P.W  =  .695  I.  H.  P.m      (6) 
i.io 

or        I.  H.  P.m  =  1.44  B.  H.  P.n  (7) 

In  the  case  of  an  engine  to  be  constructed,  B.  H.  P.n  is  usually 
specified,  hence  I.  H.  P.n  can  be  found  from  equation  (6).  Sub- 
stituting this  in  equation  (4)  leaves  as  the  unknown  factors  in 
this  equation  the  factors  I,  a,  and  n.  The  latter  depends  upon 
the  revolutions,  which  may  also  be  specified  or  determined  from 
equation  (2).  This  leaves  only  I  and  a  to  be  determined. 

It  is  next  necessary  to  find  some  relation  between  cylinder 
diameter  and  stroke.  An  examination  of  existing  engines  shows 
that  practice  in  this  regard  is  pretty,  well  settled.  High-speed 

S~f~  T*O  Kf* 

engines  show  a  ratio  of  -         — •  =  1.1  to  1.3.    In  medium  speed 
diameter 

engines  the  ratio  varies  from  about  1.2  to  1.6,  and  large 
machines  vary  between  1.5  and  2.0, 


POWER  OF  GAS  ENGINES  475 

To  determine  the  cylinder  dimensions,  let  d  be  the  diameter 
of  the  cylinder  in  feet  and  let 

/  =  x  d  (8) 

Then  equation  (4)  may  be  rewritten  for  maximum  power, 

(M.E.P.)  X  xd  X  .785  d*  X  144  X  n 
33000 


300 


From  this  the  cylinder  diameter  is 

3 


^V@iS^ft-  (10) 

EXAMPLES.  —  1.    To  show  the   method  of  using  these  equa- 
tions, suppose  it  is  desired  to  determine  the  required  cylinder 
dimensions  for  a  100  B.  H.  P.,  four-cycle  throttling  engine,  using 
anthracite  producer  gas. 
From  equation  (2),  the  number  of  revolutions  should  be  about 

1200 


From  the  table  of  Chapter  IV,  a  compression  pressure  of  120 
pounds  by  gage  is  about  normal  for  the  fuel  used.  From  Tables 
I  and  II  we  should  expect  a  mean  effective  pressure  for  this  case  of 

M.  E.  P.  =  100  X  .80  -  80  pounds. 
From  equation  (7),    I.  H.  P.m  =  1.44  B.  H.  P.n  =  1.44  X  100  =  144 

The  engine  being  of  the  throttling  type, 

r.p.m.        185 
n  =    -^—        —  =  92.5 

and  a;' may  be  assumed  equal  to  1.6. 

Substituting  these  values  in  equation  (10),  we  finally  have 


. 

=  Appr.  184" 

Stroke     =  1.6  X  18.5"  =  app.  29f" 
and         r.p.m.     =  185 


476  INTERNAL   COMBUSTION  ENGINES 

2.  A  four-cycle  gasoline  engine  has  a  cylinder  diameter  of 
6",  a  stroke  of  8i",  and  the  number  of  revolutions  is  250  per 
minute.  It  is  governed  by  hit  and  miss.  What  is  its  probable 
brake  horse-power  at  normal  load? 

The  M.  E.  P.  at  normal  I.  H.  P.  from  Tables  I  and  II  is  about 

1.12  X  75  =  84  pounds 

assuming  that  the  compression  pressure  is  about  70  pounds  by 
gage.     For  the  maximum  indicated  horse-power,  the   number  of 

r  i>m        250 
explosions  n  may  be  assumed  to  be  equal  to    'v'   ~  =  —^-  =125. 

Substituting  in  equation  (4) 

84  X  ^X  785X62X125 
I.H.P.JW=1.15LH.P.W=  144B.H.P.,= 


33()QQ 
=  6.35 

From  which  B.H.P.W=  |~  =  appr.  4.4 

II.  The  Second  Method  of  determining  mean  effective  pres- 
sure follows  steam  engine  practice,  and  is  developed  in  detail  by 
Lucke  in  his  Gas  Engine  Design.  The  method  consists  of  draw- 
ing first  a  standard  air  reference  diagram.  From  this  the  mean 
effective  pressure  is  determined  by  multiplying  the  mean  effective 
pressure  of  the  standard  diagram  by  a  card  or  diagram  factor 
depending  upon  the  kind  of  fuel  used  and  the  compression  carried. 
Thus  fundamentally  this  method  does  not  differ  greatly  from 
that  of  Moss  outlined  above. 

The  standard  air  reference  diagram  is  obtained  by  working 
a  pound  of  air,  which  is  assumed  to  receive  as  much  heat  as  a 
pound  of  the  proper  fuel-air  mixture  to  be  used  in  the  real  engine 
would  contain,  through  the  cycle. 

The  following  table  shows  the  card  factors  as  determined  by 
Lucke  from  a  large  number  of  constructed  engines: 


POWER  OF  GAS  ENGINES 


477 


Kind  of  Fuel  and  Method  of  Use 

Range  of 
Compression 
by  Gage 

Card  Factor 

% 

Kerosene,  when  previously  vaporized  
Kerosene,  injected  on  hot  bulb,  may  be  as  low  as  
Gasoline,  used  in  carbureter  requiring   a  vacuum,  de- 
pending upon  the  extent  of  the  vacuum 

45-75 

30-40 
20 

25-40 

Gasoline  with  but  little  initial  vacuum 

80-130 

50-30 

100-160 

56-40 

Coal  gas             

Av.  80 

Av  45 

Blast  furnace  gas                                                              .... 

130-180 

48-30 

Natural  gas                                                                       .... 

90-140 

52-40 

NOTE.  —  Card  factors  for  two-cycle  engines  may  be  taken  as  .8  that  for 
four-cycle  machines. 

The  mean  effective  pressure  of  the  standard  air  reference 
diagram,  of  course  increases  continuously  with  the  compression. 
The  above  table,  however,  shows  that  the  card  factor  decreases  as 
the  compression  increases  for  all  fuels  except  kerosene.  This 
accounts  for  the  fact  that  in  Moss's  Table  I  the  M.  E.  P.  does  not 
increase  beyond  certain  compressions.  The  thermal  and  mechan- 
ical reasons  underlying  this  fact  have  been  explained  in  Chap.  IV. 

The  table  of  card  factors  shows  a  large  range  of  variation  in 
the  different  factors  and  emphasizes  the  point  made  by  Lucke 
that  in  determining  cylinder  sizes  a  great  deal  must  be  left  to  the 
personal  experience  and  judgment  of  the  designer. 

III.  Third  Method  of  Determining  Cylinder  Dimensions.  It 
must  be  obvious  from  what  has  been  said  that  it  is  not  at  all 
easy  to  predict  with  fair  accuracy  the  mean  effective  pressure 
an  engine  may  be  expected  to  realize.  For  that  reason  a  method 
of  determining  the  cylinder  dimensions  of  a  proposed  engine,  or 
the  power  of  an  existing  engine,  without  first  determining  the 
M.  E.  P.,  should  be  welcome. 

The  method,  developed  by  Giildner,*  is  based  upon  two  well- 
known  facts: 

1.  The  power  developed  by  any  gas  engine  depends  directly 
upon  the  volume  of  the  mixture  it  can  handle  in  unit  time. 

2.  The  power  also  depends  upon  the  thermal  efficiency  with 
which  the  engine  can  handle  this  volume  of  mixture. 

Regarding  the  first   point,  the  charge  volume  in  unit  time 


*  Giildnor,  Entwerfon  &  Berechnen  der  Verbrennungsmotoren. 


478  INTERNAL  COMBUSTION  ENGINES 

involves  cylinder  diameter,  stroke,  and  number  of  revolutions. 
Two  of  these  factors  can  usually  be  fixed  upon,  which  determines 
the  third.  The  computation  of  the  charge  volume  for  a  given 
time  involves  the  assumption  of  a  value  for  the  volumetric  effi- 
ciency of  the  suction  stroke.  There  is  now  so  much  experimental 
data  regarding  this  point  that  no  great  error  can  be  made.  A 
table  of  volumetric  efficiencies  Ev  for  various  types  of  engines  is 
given  on  page  86. 

The  same  is  true  of  the  thermal  efficiency  and  fuel  characteris- 
tics. A  large  number  of  tests  on  various  types  of  machines  and 
different  fuels  enables  us  to-day  to  forecast  with  a  fair  degree 
of  accuracy  what  thermal  efficiency  may  be  expected  from  a 
given  engine  when  its  approximate  power  and  the  kind  of  fuel 
used  are  known. 

The  following  derivation  of  equations  for  values  of  diameter, 
stroke  and  revolutions  per  minute  is  due  to  Giildner,*  as  is  also 
the  appended  table.  All  metric  measurements  and  values  have 
been  transformed  to  English  units: 

Let  B.  H.  P.n  or  Nn  =  nominal  brake  horse-power. 
n      =  R.  P.  M. 

d     =  piston  diameter  in  feet. 
/      =  stroke  in  feet. 
Vh  =  .785  dH  =  piston  displacement  per  stroke 

in  cu.  ft. 
V     =  EvVh  =  actual  volume  of  mixture  in  cu.  ft. 

per    suction    stroke,    barometer    28.95", 

temperature  59  degrees  Fahrenheit. 
y 
Ev  =  —  =  volumetric  efficiency  of  suction  stroke. 

L  =  the  volume  of  air  in  cu.  ft.  required  for 
1  cu.  ft.  of  gas  fuel,  or  1  pound  of  liquid 
fuel,  under  most  favorable  practical  con- 
ditions. This  is  not  the  theoretical  quan- 
tity, but  some  excess  quantity  as  seems 
best  for  the  particular  fuel. 

*  The  article  may  be  found  either  in  the  Zeitschrift  des  Vereines  deut- 
scher  Ingenieure,  April  26,  1902,  or  in  his  book,  Entwerfen  und  Berechnen 
der  Verbrennungsmotoren,  pp.  213-215. 


POWER  OF  GAS  ENGINES  479 

Lh  =  the    resulting    actual    quantity    of   air   in 

cu.    ft.    for   one   explosion,    for   nominal 

horse-power. 
Cs   =  the   quantity  of  fuel  used   per  hour,   for 

gases  in  cu.  ft.,  for  liquids  in  pounds,  at 

nominal  horse-power. 
C    =  the  same  per  horse-power  hour. 
Ch  •=  the  same  per  explosion. 
H    =  the  lower  heating  value  of  the   fuel,   for 

gases  per  cu.  ft.,  for  liquids,  per  pound, 

in  B.  T.  U. 

_  Nn  X  33000  X  60  _  2545  Nn_  (  thermal     efficiency    at     the 
778  CSH  CSH         (  brake  =  economic  efficiency. 

From  the  above  we  can  derive  for  four-cycle  engines 

Nn  X  33000  X  60      2545  Nn 
778  He  ~TU~ 

_2CJ_2X2545JV»      84.8AT, 
60  n          60  nHe  nHe 

CSL  _  2545  NnL  _  84.8  NnL 
h      30  n         30  nHe  nHe 

For  two-cycle  engines  equations  (12)  and  (13)  should  be 
divided  by  2,  because  there  is  a  charging  stroke  for  every  revolu- 
tion. 

ENGINES    FOR    GAS    FUEL 

The  actual  charge  taken  in  by  the  engine  during  one  suction 
stroke  must  be 

v  -  c*  +  ^ 

This  volume  requires  a  piston  displacement  of 

V  -  Ch  +  Lh  _  84.8  Nn  +  84.8  NnL 

V   ~  - 


(14) 


Ev  nHeEv 

84.8  #»(!  +  L) 


nHeEv 
Solving  (14)  for  d,  I  and  n  in'  turn,  we  have 


480  INTERNAL  COMBUSTION  ENGINES 


ENGINES    FOR    LIQUID    FUEL 

In  this  case  the  fuel  is  introduced  either  in  liquid  form  or  in 
the  shape  of  vapor.  In  either  case  the  volume  ratios  of  fuel  to 
air  are  very  much  smaller  than  they  are  in  the  case  of  gaseous 
fuels.  Take  for  instance  the  case  of  alcohol,  a  fuel  of  low  heating 
value.  Here  we  find  that  the  vapor  does  not  form  theoretically 
more  than  4  per  cent  of  the  volume  of  the  charge.  In  reality  it 
is  even  less  than  this  on  account  of  the  excess  air  used.  In  view 
of  this  fact  we  may  put  for  these  engines 


.785  d*l  =       =      'n    cubic  feet  (18) 


Solving  this  again  for  d,  I  and  n  we  obtain  for  engines  using 
liquid  fuel: 

-  «•» 

«> 

In  these  equations  the  quantities  to  which  certain  values 
must  be  assigned  are  L,  e  and  Elv.  As  stated  before,  there  is  now 
so  much  practical  data  at  hand  that  the  proper  determination  of 
these  should  cause  no  difficulty.  For  values  of  Ev  see  Table, 
p.  86.  The  table  on  the  opposite  page  gives  values  of  L,  C  and 
e,  as  found  for  various  fuels. 

Since  the  nominal  brake  horse-power  Nn  is  18  to  20  per  cent 
below  the  maximum  capacity  of  engines  in  ordinary  cases,  it  is 
well  to  assume  an  excess  of  air  of  about  30  per  cent  at  the  outset, 
in  the  case  of  machines  using  gas.  In  the  case  of  liquid  fuel 


POWER  OF  GAS  ENGINES 


481 


a 
H 

Q 

B 

< 

rf 
p 

o 
E  || 

PS    0 

Sz 


SI 

« 


to    to   i— i    t>- 
00    CO    to    CO 


00     T*     00     TjH     -^     CO          .tO          . 

;  co    ;  ; 
8    :S    :    :    :    :|    : : 

.  c^    .  co  oo  t>-    \    '.    ; r 

;   CO      ;   I-H   00  Tf      ;      ;      ;  ; 

T-H  c^  i- i  <N  <N  ?5    ;  co    ;  ! 

~o    r^    T~.    ;    TCSJ    ;    ;    r 

^    :  ^    '•    '•    '•    '•  -#    '•  '• 

.    CO       .    00   O    -^       .       .       . 
'   t>      •    Tj5   (N   CO      *  /  ' 
;  i>     ;  oo  o  <N     ;     ;     ; 

C^       .    C1^       .       .       .    Oi    —    ^O  O^ 

.  oq     .  oq  p  p     !     '.     '.  7 

•     Tf          '     i-H     CO     O 

;  oo     ;  o>  I-H  co     ;     ;     ; 

•  w    .  p  p  co    ;    ;    ;  r 

i— I     i-H     T— I     i— (         !         !     rH     C^     >— ^  C^l 

10     '.  co     '.     '.     '.  to  to  co  o 

i— I          '     i— I          •          •          •     i— I  r* 

§•    co      • 
'    rH 

'•    T    ;     :     '.     .  co  co  co  co~ 

to    C^    (N  O5 

«O   00    ^  (N 


CO    CO   CO    CO 
<N    C^    (N    (N 


nn    CO    O5    »O 

d  06  co  »d 

(N     -H      l-l     l-l 


-X 
p 
fe 


(N    i— i    CO    t^ 


(N    (N    (N    <M 


to      o      to 
to     -^     co 


<>m 


to  o  oo  to 

tO   to   CO   CO 


i— i       •    OS   CO 
Tt<       -(NO 


>-,         .     ow««  .     v  -S 

M                .       ^       O  j,      -»S  W 

'5    22  -S  '«  -2 

's  €  e  1 1. 1 1 


cu  ^ 

g  fl 
o  o 


P  73    O    c 
O     3     S     « 

Woo^ 


O    ^3    I-H    >.'    J>    I— I    tH    »-H 

-H«    >C:K 


482  INTERNAL  COMBUSTION  ENGINES 

engines  a  greater  excess,  50  to  60  per  cent,  should  be  used,  because 
these  fuels  are  usually  high  in  heating  value,  and  if  any  economi- 
cal degree  of  compression  is  to  be  employed,  the  fuel  mixture 
should  be  rather  lean.  Besides  it  is  not  easy  to  produce  a  uniform 
fuel  mixture  in  the  case  of  liquid  fuels,  and  an  excess  of  air  would 
help  to  overcome  this  difficulty.  These  excess  air  allowances 
have  been  made  in  the  table.  The  values  of  C  and  e  are  for  the 
various  fuels  and  for  various  sizes  of  engines,  as  determined  from 
existing  data.  The  fuel  consumed  by  heating  apparatus  and 
ignition  flames  is  not  included  in  C.  In  the  case  of  engines  using 
generator  gas  it  is  supposed  that  suction  generators  are  employed 
requiring  no  fuel  for  a  separate  boiler. 

To  see  how  the  results  obtained  by  Giildner's  method  agree 
with  those  obtained  by  Moss,  the  same  examples  will  be  taken. 

EXAMPLE  1.  —  Engine  to  be  100  B.  H.  P.,  throttling  governor, 
fuel  to  be  anthracite  producer  gas.  Determine  the  cylinder 
dimensions,  assuming  as  before  that  the  number  of  revolutions 
is  185  per  minute. 

For  this  case  any  one  of  the  formulae  15  to  17  may  be  used. 
Taking  the  first,  we  have 


in  which     Nn  =  100  B.  H.  P. 

L     =  air  used  per  cu.  ft.  of  the  fuel  gas  =  say  1.3  for 

anthracite  gas  from  the  table. 
e      =  thermal  efficiency  that  may  be  expected  =  .24 

from  the  table. 
n      =  185. 
H     =  heating  value  of  fuel  =  141   B.  T.  II.  from  the 

table. 
I      =  Stroke  =  x  d  =  assumed  as   1.6  d  in  previous 

case. 
Ev  ==  volumetric  efficiency  =  say  .90  from  table  p.  86. 

The,  ff-  108  X  10°  X  2'3 


-24X.185X  141  X  1.6  dX  .90 

rf3  = 108X100X2.3 

.24  X  185  X  141  X  1.6  X  .90 


POWER  OF  GAS  ENGINES  483 

from  which  d  =  1.42  ft.  =  appr.  17",  and 

I   =  1.6  d  =  1.6  X  17"  =  appr.27i". 

This  method,  therefore,  apparently  calls  for  a  smaller  engine. 
EXAMPLE  2.  —  Gasoline    engine,    cyl.    diam.    6",   stroke    8J", 
r.p.rrr.  250.     Hit-and-miss  governor.     Determine  probable  B.  H.  P. 
For  this,  equation  21  may  be  rewritten 

_  nelHd?Ev 
108  L 

in  which     n    =  250  r.p.m. 

e     =  thermal  efficiency  =  .19  from  table. 

I      -  stroke  -  8J"  =  .71  ft. 

H   ==  heating  value  of  fuel  =  19800,  from  table. 

d     =  6"  -  .5  ft.,  d2  =  .25. 

j£v  =  .75,  from  p.  86,  since  this  engine  is  likely  to  have 
an  automatic  inlet  valve. 

L     =  250,  for  a  good  rich  mixture. 
Then 

250  X  .19  X  .71  X  19800  X  .25  X  .75  ^  „  p 

^=  108  X  250 

The  previous  example  gave  4.4  B.  H.  P.  so  that  the  agreement 
in  this  case  is  satisfactory. 

IV.  For  determining  the  power  rating  of  automobile  engines, 
several  more  or  less  empirical  formula  are  in  use,  two  of  which 
will  be  cited. 

The  Association  of  Automobile  Manufacturers  has  fixed  upon 
the  following  expression  for  four-cycle  engines: 


where      d    =  diameter  of  cylinder  in  inches,  and 
N  =  number  of  cylinders. 

This  is  based  on  a  speed  of  1000  r.p.m.  In  this  formula, 
however,  the  factor  2.5  results  from  the  contraction  of  several 
other  factors  more  or  less  arbitrarily  assumed,  and  hence  as  far 
as  design  is  concerned  the  formula  is  of  little  or  no  use. 


484  INTERNAL  COMBUSTION  ENGINES 


where      d    =  cyl.  diam.  in  inches. 
I    =  stroke  in  inches. 
TV  =  no.  of  cylinders. 
n    =  r.p.m.,  and 
Cl  =  clearance  expressed  in  terms  of  piston  displacement. 

The  following  example  shows  the  application  of  the  methods 
discussed  to  the  determination  of  the  power  of  an  automobile 
machine. 

EXAMPLE.  —  Cylinder  diameter  4",  stroke  4£",  r.p.m.  1000, 
no.  of  cylinders  4.  Determine  the  probable  B.  H.  P. 

I.    By  determination  of  M.  E.   P. 

Assume  compression  carried  is  80  pounds,  which  requires 
about  28  per  cent  clearance.  From  Moss's  Tables 

M.  E.  P.  =  75  X  1.12  =  84  pounds. 
From  equation  (4)  therefore 

84  X  ~  X  .785  X  42  X  500 
LH'P-  ' 


33000  ' 

Since  the  mechanical  efficiency  is  in  the  neighborhood  of  .80, 

B.  H.  P.  =  .8  X  6  =  4.8 
and  for  four  cylinders 

Total    B.  H.  P.  =  4  X  4.  8  =  19,2 
II.    By  Giildner's  Method: 

nelHd2Ev 
108  L 


Nn  =  - 


1000  X  .20  X  ^  X  19800  X  (AYx  -75 

= ±£ ylJ/ =  46 

108  X  250 

and  total  B.  H.  P.  =  4  X  4.6  -  18.4 
III.    By  Association  Formula: 


POWER  OF  GAS  ENGINES  485 

IV.    By  Rice's  Formula: 

4' X  4.5  X  4  X  IQOO/  _J \ 

14000  {•*    h10X.28j- 

Of  the  above  results,  those  obtained  by  methods  I,  II,  and  IV 
agree  very  well.  Method  III  gives  a  result  considerably  higher, 
but  in  view  of  the  fact  that  the  choice  of  the  factor  2.5  is  some- 
what arbitrary,  this  discrepancy  does  not  mean  much.  If  the 
factor  had  been  taken  equal  to  three,  for  instance,  as  is  sometimes 
done,  the  result  would  be.  brought  down  to  21.3  horse-power 
which  is  not  so  far  different  from  the  rest. 


CHAPTER   XVI 

METHODS    OF   TESTING    GAS    ENGINES 

THE  actual  testing  of  gas  engines,  that  is,  the  determination  of 
indicated  and  brake  horse-power,  speed,  fuel  consumption,  etc.,  does 
not  differ  materially  from  the  methods  long  become  standard  in 
steam  engine  practice.  But  the  calculations  involved  in  the  proper 
working  up  of  the  data  obtained  are  enough  different  to  have  caused 
engineering  societies  at  home  and  abroad  to  set  up  rules  and  regu- 
lations, so-called  codes,  for  testing  internal  combustion  engines. 

Thus  in  1898  the  American  Society  of  Mechanical  Engineers 
appointed  a  committee  for  this  purpose  which  rendered  a  final 
report  in  an  Appendix  to  the  Steam  Engine  Code  in  1901.  The 
British  Institution  of  Civil  Engineers  followed  suit,  the  pre- 
liminary and  final  reports  being  rendered  in  March  and  December, 
1905,  respectively.  Finally  the  Verein  Deutscher  Ingenieure 
adopted  a  code  for  the  testing  of  gas  engines  and  gas  producers, 
which  was  published  in  the  Zeitschrift  for  November  24,  1906. 
The  latter  code  was  translated  nearly  entirely  by  Mr.  F.  E.  Junge 
and  will  be  found  in  Power  for  February,  1907. 

Of  these  codes  the  American  and  German  give  specific  rules 
for  testing,  the  latter  paying  particular  attention  to  acceptance 
tests  of  both -engines  and  gas  producers.  The  British  report 
concerns  itself  mainly  with  establishing  efficiency  standards. 

In  describing  the  methods  followed  in  the  testing  of  gas 
engines,  it  was  thought  best  to  give  the  American  code  in  its 
entirety,  supplementing  it  by  most  of  the  references  to  the  steam 
engine  code  contained  in  its  original  printed  form.  This  is  fol- 
lowed by  a  translation  of  nearly  the  entire  German  code,  modi- 
fied where  necessary  to  suit  the  American  conditions.  This 
code  is  also  given  because  it  not  only  supplements  the  American 
code  in  some  important  details,  but  on  account  of  the  rules  given 
for  the  testing  of  gas  producers. 

480 


METHODS  OF  TESTING  GAS  ENGINES          4s? 


RULES  FOR  CONDUCTING  TESTS  OF  GAS  AND  OIL  ENGINES.       CODE,  OF 

1901 

I.  Objects  of  the  Tests.  —  At  the  outset  the  specific  object 
of  the  test  should  be  ascertained,  whether  it  be  to  determine  the 
fulfilment  of  a  contract  guarantee,  to  ascertain  the  highest  econ- 
omy obtainable,  to  find  the  working  economy  and  the  defects  as 
they  exist,  to  ascertain  the  performance  under  special  conditions, 
or  to  determine  the  effect  of  changes  in  the  conditions;  and  the 
test  should  be  arranged  accordingly. 

Much  depends  upon  the  local  conditions  as  to  what  prepara- 
tions should  be  made  for  a  test,  and  this  must'  be  determined 
largely  by  the  good  sense,  tact,  judgment,  and  ingenuity  of  the 
expert  undertaking  it,  keeping  in  mind  the  main  issue,  which  is 
to  obtain  accurate  and  reliable  data.  In  deciding  questions  of 
contract,  a  clear  understanding  in  regard  to  the  methods  of  test 
should  be  agreed  upon  beforehand  with  all  parties,  unless  these 
are  distinctly  provided  for  in  the  contract. 

II.  General  Condition  of  the  Engine.  —  Examine  the  engine, 
and  make  notes  of  its  general  condition,  and  any  points  of  design, 
construction,  or  operation  which  bear  on  the  objects  in  view. 
Make  a  special  examination  of  all  the  valves  by  inspecting  the 
seats  and  bearing  surfaces,  and  note  their  condition,  and  see  if  the 
piston  rings  are  gas-tight. 

If  the  trial  is  made  to  determine  the  highest  efficiency,  and 
the  examination  shows  evidence  of  leakage,  the  valves  and  piston 
rings,  etc.,  should  be  made  tight,  and  all  parts  of  the  engine  put 
in  the  best  possible  working  condition  before  starting  on  the  test. 

III.  Dimensions,  etc.  —  Take  the  dimensions  of  the  cylinder, 
or  cylinders,  whether  already  known  or  not;  this  should  be  done 
when  they  are  hot,  and  in  working  order.     If  they  are  slightly 
worn   the   average'  diameter   should   be   determined.      Measure, 
also,  the  compression  space  or  clearance  volume,  which  should  be 
done,  if  practicable,  by  filling  the  spaces  with  water  previously 
measured,  the  proper  correction  being  made  for  the  temperature. 

IV.  Fuel.  —  Decide  upon  the  gas  or  oil  to  be  used,  and  if  the 
trial  is  to  be  made  for  maximum  efficiency,  the  fuel  should  be  the 
best  of  its  class  that  can  readily  be  obtained,  or  one  that  shows 
the  highest  calorific  power. 


488  INTERNAL  COMBUSTION  ENGINES 

V.    Calibration    of    Instruments    used    in    the    Tests.  —  All 

instruments  and  apparatus  should  be  calibrated  and  their  re- 
liability and  accuracy  verified  by  comparison  with  recognized 
standards.  Apparatus  liable  to  change  or  to  become  broken 
during  the  tests,  such  as  gages,  indicator  springs,  and  ther- 
mometers, should  be  calibrated  both  before  and  after  the  experi- 
ments. The  accuracy  of  all  scales  should  be  verified  by  standard 
weights.  In  the  case  of  gas  or  water  meters,  special  attention 
should  be  given  to  their  calibration,  both  before  and  after  the 
trial,  and  at  the  same  rate  of  flow  and  pressure  as  exists  during 
the  trial. 

(a)  GAGES.  —  For    pressures    above  the  atmosphere,  one  of 
the  most  convenient,  and  at  the  same  time  reliable,  standards  is 
the   dead-weight   testing   apparatus   which   is   manufactured   by 
many  of  the  prominent  gage  makers.       It   consists  of  a  vertical 
plunger  nicely  fitted  into  a  cylinder  containing  oil  or  glycerine, 
through  the  medium  of  which  the  pressure  is  transmitted  to  the 
gage.      The  plunger  is  surmounted  by  a  circular  stand  on  which 
weights  may  be  placed,  and  by  means  of  which  any  desired  pres- 
sure can  be  secured.     The  total  weight,  in  pounds,  on  the  plunger 
at  any  time,  divided  by  the  area  of  the  plunger  and  of  the  bush- 
ing which  receives  it,  in  square  inches,  gives  the  pressure  in  pounds 
per  square  inch. 

Another  standard  of  comparison  for  pressures  is  the  mercury 
column.  If  this  instrument  is  used,  assurance  must  be  had  that 
it  is  properly  graduated  with  reference  to  the  ever  varying  zero 
point;  that  the  mercury  is  pure,  and  that  the  proper  correction 
is  made  for  any  difference  of  temperature  that  exists,  compared 
with  the  temperature  at  which  the  instrument  was  graduated. 

For  pressure  below  the  atmosphere,  an  air 'pump  or  some 
other  means  of  producing  a  vacuum  is  required,  and  reference 
must  be  made  to  a  mercury  gage.  Such  a  gage  may  be  a 
U-tube  having  a  length  of  30  inches  or  so,  with  both  arms  properly 
filled  with  pure  mercury. 

(b)  THERMOMETERS.  —  Standard    thermometers    are    those 
which  indicate  212  degrees  Fahrenheit  in  steam  escaping  from 
boiling  water  at  the  normal  barometrical  pressure  of  29.92  inches, 
the  whole  stem  up  to  the  212-degree  point  being  surrounded  by 
the  steam;  and  which  indicate  32  degrees  Fahrenheit  in  melting 


METHODS  OF  TESTING  GAS  ENGINES  489 

ice,  the  stem  being  likewise  completely  immersed  to  the  32-de- 
gree  point;  and  which  are  calibrated  for  points  between  and 
beyond  these  two  references  points.  We  recommend,  for  tem- 
peratures between  212  degrees  and  400  degrees  Fahrenheit,  that 
the  comparison  of  the  thermometer  be  made  with  the  tempera- 
ture given  in  Regnault's  Steam  Tables,  the  method  required 
being  to  place  it  in  a  mercury  well  surrounded  by  saturated  steam 
under  sufficient  pressure  to  give  the  right  temperature.  The 
pressure  should  be  accurately  determined  as  pointed  out  in  the 
above  section  (a),  and  the  thermometer  should  be  immersed  to 
the  same  extent  as  it  is  under  its  working  condition. 

Thermometers  in  practice  are  seldom  used  with  the  stems 
fully  immersed;  consequently,  when  they  are  compared  with  the 
standard,  the  comparison  should  be  made  under  like  conditions, 
whatever  those  happen  to  be. 

If  pyrometers  of  any  kind  are  used,  they  should  be  compared 
with  a  mercury  thermometer  within  its  range,  and  if  extreme 
accuracy  is  required  with  an  air  thermometer,  or  a  standard 
based  thereon,  at  higher  points,  care  being  taken  that  the  medium 
surrounding  the  pyrometer,  be  it  air  or  liquid,  is  of  the  same 
uniform  temperature  as  that  surrounding  the  standard. 

(c)  INDICATOR  SPRINGS.  —  The  indicator  springs  should  be 
calibrated  with  the  indicator  in  as  nearly  as  possible  the  same 
condition  as  to  temperature  as  exists  during  the  trial.  This 
temperature  can  usually  be  estimated  in  any  particular  case.  A 
simple  way  of  heating  the  indicator  is  to  subject  it  to  a  steam 
pressure  just  before  calibration.  Compressed  air,  or  compressed 
carbonic  acid  gas,  are  suitable  for  the  actual  work  of  calibration. 
These  gases  should  .be  used  in  preference  to  steam,  so  as  to  bring 
the  conditions  as  near  as  possible  to  those  which  obtain  when 
the  indicators  are  in  actual  use.  When  compressed  carbonic 
acid  gas  is  used,  and  trouble  arises  from  the  clogging  of  the  escape 
valves  with  ice,  the  pipe  between  the  valve  and  the  gas  tank 
should  be  heated.  With  both  air  and  carbonic  acid  gas,  the 
pipes  leading  to  the  indicator  should  also  be  heated  if  it  is  found 
that  they  are  below  the  required  temperature.  The  springs  may 
be  calibrated  for  this  class  of  engines  under  a  constant  pressure, 
if  desired,  and  the  most  satisfactory  method  is  to  cover  the  whole 
range  of  pressure  through  which  the  indicator  acts;  first,  by  grad- 


490  INTERNAL  COMBUSTION  ENGINES 

ually  increasing  it  from  the  lowest  to  the  highest  point,  and  then 
gradually  reducing  it  from  the  highest  to  the  lowest  point,  in  the 
manner  which  has  heretofore  been  widely  followed  by  indicator 
makers;  a  mean  of  the  results  should  be  taken.  The  calibration 
should  be  made  for  at  least  five. points,  two  of  these  being  for  the 
pressures  corresponding  to  the  maximum  and  minimum  pressures, 
and  three  for  intermediate  points  equally  distant. 

The  standard  of  comparison  recommended  is  the  dead  weight 
testing  apparatus,  a  mercury  column,  or  a  steam  gage,  which 
has  been  proved  correct  by  reference  to  either  of  these  standards. 

When  the  scale  of  the  spring  determined  by  calibration  is 
found  to  vary  from  the  nominal  scale  with  substantial  uniformity, 
it  is  usually  sufficiently  accurate  to  take  the  arithmetical  mean 
of  the  scales  found  at  the  different  pressures  tried.  When,  how- 
ever, the  scale  varies  considerably  at  the  different  points,  and 
absolute  accuracy  is  desired,  the  method  to  be  pursued  is  as 
follows:  Select  a  sample  diagram  and  divide  it  into  a  number  of 
parts  by  means  of  lines  parallel  to  the  atmospheric  line,  the 
number  of  lines  being  equal  to  and  corresponding  with  the  num- 
ber of  points  at  which  the  calibration  of  the  spring  is  made. 
Take  the  mean  scale  of  the  spring  for  each  division  and  multiply 
it  by  the  area  of  the  diagram  inclosed  between  two  contiguous 
lines.  Add  all  the  products  together  arid  divide  by  the  area  of 
the  whole  diagram;  the  result  will  be  the  average  scale  of  the 
spring  to  be  used.  If  the  sample  diagram  selected  is  a  fair  repre- 
sentative of  the" entire  set  of  diagrams  taken  during  the  test,  this 
average  scale  can  be  applied  to  the  whole.  If  not,  a  sufficient 
number  of  samples  of  diagrams  representing  the  various  conditions 
can  be  selected,  and  the  average  scale  determined  by  a  similar 
method  for  each,  and  thereby  the  average  for  the  whole  run. 

(d)  GAS  METERS.  —  A  meter  used  for  measuring  gas  for  a 
gas  engine  shouW  be  calibrated  by  referring  its  readings  to  the 
displacement  of  a  gasometer  of  known  volume,  by  comparing  it 
with  a  standard  gas  meter  of  known  error,  or  by  passing  air 
through  the  meter  from  a  tank  in  which  air  under  pressure  is 
stored.  If  the  latter  method  is  adopted,  it  is  necessary  to  observe 
the  pressure  of  the  air  in  the  tank  and  its  temperature,  both  at 
the  tank  and  at  the  meter,  and  this  should  be  done  at  uniform 
intervals  during  the  progress  of  the  calibration.  The  amount  of 


METHODS  OF  TESTING  GAS  ENGINES 


491 


air  passing  through  the  meter  is  computed  from  the  volume  of 
the  tank  and  the  observed  temperatures  and  pressures. 

The  volume  of  the  gas  thus  ascertained  should  be  reduced  to 
the  equivalent  at  a  given  temperature  and  atmospheric  pressure, 
corrected  for  the  effect  of  moisture  in  the  gas,  which  is  ordinarily 
at  the  saturation  point  or  nearly  so.  We  recommend  that  a 
standard  be  adopted  for  gas-engine  work,  the  same  as  that  used 
in  photometry,  namely,  the  equivalent  volume  of  the  gas  when 
saturated  with  moisture  at  the  normal  atmospheric  pressure  at  a 
temperature  of  60  degrees  Fahrenheit.  In  order  to  reduce  the 
reading  of  the  volume  containing  moist  gas  at  any  other  tempera- 
ture to  this  standard,  multiply  by  the  factor 

459.4  +  60      b  -  (29.92  -  s) 


459.4  +   t 


X 


29.4 


CALIBRATION  OF  A  WATER  METER 
SKETCH  SHOWING  METER  CONNECTIONS  ETC% 


in  which  b  is  the  height  of  the  barometer  in  inches  at  32  degrees 
Fahrenheit,  t  the  temperature  of  the  gas  at  the  meter  in  degrees 
Fahrenheit,  and  s  the  vacuum  in  inches  of  mercury  corresponding 
to  the  temperature  of  t  obtained  from  steam  tables. 

(e)  WATER  METERS.  —  A  good  method  of  calibrating  a  water 
meter  is  the  following,  reference  being  made  to  Fig.  16-1. 

Two  tees  A  and  B  are  placed  in  the  feed  pipe,  and  between 
them  two  valves  C  and  D.*  The  meter  is  connected  between  the 
outlets  of  the  tees  A 
and  B.  The  valves 
E  and  F  are  placed 
one  on  each  side  of 
the  meter.  When  the 
meter  is  running, 
the  valves  E  and  F 
are  opened,  and  the 
valves  C  and  D  are 
closed.  Should  an 
accident  happen  to 
the  meter  during  the 
test,  the  valves  E 
and  F  may  be  closed, 
and  the  valves  C  and  D  opened,  so  as  to  allow  the  feed  water 
to  flow  directly  to  the  point  of  use.  A  small  bleeder  G  is 


FIG.  16-1. 


492  INTERNAL  COMBUSTION  ENGINES 

opened  when  the  valves  C  and  D  are  closed,  in  order  to  make 
sure  that  there  is  no  leakage.  A  gage  is  attached  at  H.  When 
the  meter  is  tested,  the  valves  C,  D,  and  F  are  closed,  and  the 
valves  E  and  /  are  opened.  The  water  flows  from  the  valve 
/  to  a  tank  placed  on  weighing  scales.  In  testing  the  meter  the 
rate  of  flow  should  be  the  same  as  that  on  test,  and  the  water 
leaving  the  meter  is  throttled  at  the  valve  /  until  the  pressure 
shown  by  the  gage  H  is  the  same  as  that  indicated  when  the 
meter  is  running  under  the  normal  conditions.  The  piping  lead- 
ing from  the  valve  /  to  the  tank  is  arranged  with  a  swinging  joint, 
consisting  merely  of  a  loosely  fitting  elbow,  so  that  it  can  be  swung 
readily  into  the  tank  or  away  from  it.  After  the  desired  pressure 
and  rate  of  flow  have  been  secured,  the  end  of  the  pipe  is  swung 
into  the  tank  the  instant  that  the  pointer  of  the  meter  is  opposite 
some  graduation  mark  on  the  dial,  and  the  water  continues  to 
empty  into  the  tank.  The  tests  should  be  made  by  starting  and 
stopping  at  the  same  graduation  mark  on  the  meter  dial,  and 
continued  until  at  least  10  or  20  cubic  feet  are  discharged  for  one 
test.  The  water  collected  in  the  tank  is  then  weighed. 

The  water  passing  the  meter  should  always  be  under  pressure 
in  order  that  any  air  in  the  meter  may  be  discharged  through  the 
vents  provided  for  this  purpose.  Care  should  be  taken  that  there 
is  no  air  contained  in  the  water.  The  meter  should  be  tested 
both  before  and  after  the  engine  trial,  and  several  tests  be  made 
of  the  meter  in  each  case  in  order  to  obtain  confirmative  results. 
It  is  well  to  make  preliminary  tests  to  determine  whether  the 
meter  works  satisfactorily  before  connecting  it  up  for  an  engine 
trial.  The  results  should  agree  with  each  other  for  two  widely 
different  rates  of  flow. 

VI.  Duration  of  Test.  —  The  duration  of  a  test  should 
depend  upon  its  character  and  the  objects  in  view,  and  in  any 
case  the  test  should  be  continued  until  the  consecutive  readings 
of  the  rates  at  which  oil  or  gas  is  consumed,  taken  at  say  half- 
hourly  intervals,  become  uniform  and  thus  verify  each  other.  If 
the  object  is  to  determine  the  working  economy,  and  the  period 
of  time  during  which  the  engine  is  usually  in  motion  is  some  part 
of  twenty-four  hours,  the  duration  of  the  test  should  be  fixed  for 
this  number  of  hours.  If  the  engine  is  one  using  coal  for  generat- 
ing gas,  the  test  should  cover  a  long  enough  period  to  determine 


METHODS  OF  TESTING  GAS  ENGINES  493 

with  accuracy  the  coal  used  in  the  gas  producer;  such  a  test  should 
be  of  at  least  twenty-four  hours'  duration,  and  in  most  cases  it 
should  extend  over  several  days. 

VII.  Starting  and  Stopping  a  Test.  —  In  a  test  for  deter- 
mining the  maximum  economy  of  an  engine,  it  should  first  be 
run  a  sufficient  time  to  bring  all  the  conditions  to  a  normal  and 
constant  state.     Then  the  regular  observations  of  the  test  should 
begin,  and  continue  for  the  allotted  time. 

If  a  test  is  made  to  determine  the  performance  under  working 
conditions,  the  test  should  begin  as  soon  as  the  regular  prepara- 
tions have  been  made  for  starting  the  engine  in  practical  work, 
and  the  measurements  should  then  commence  and  be  continued 
until  the  close  of  the  period  covered  by  the  day's  work. 

VIII.  Measurement  of  Fuel.  —  If  the  fuel  used  is  coal  fur- 
nished to  a  gas  producer,  the  same  methods  apply  for  determining 
the  consumption  as  are  used  in  steam  boiler  tests. 

If  the  fuel  used  be  gas,  the  only  practical  method  of  measure- 
ment is  the  use  of  a  meter  through  which  the  gas  is  passed.  Gas 
bags  should  be  placed  between  the  meter  and  the  engine  to  dimin- 
ish the  variation  of  pressure,  and  these  should  be  of  a  size  propor- 
tionate to  the  quantity  used.  When  a  meter  is  employed  to 
measure  the  air  used  by  an  engine,  a  receiver  with  a  flexible 
diaphragm  should  be  placed  between  the  engine  and  the  meter. 
The  temperature  and  pressure  of  the  gas  should  be  measured,  as 
also  the  barometric  pressure  and  temperature  of  the  atmosphere, 
and  the  quantity  of  gas  should  be  determined  by  reference  to  the 
calibration  of  the  meter,  taking  into  account  the  temperature 
and  pressure  of  the  gas.  (See  Section  V  (d)). 

If  the  fuel  is  oil,  this  can  be  drawn  from  a  tank  which  is  filled 
to  the  original  level  at  the  end  of  the  test,  the  amount  of  oil  re- 
quired for  so  doing  being  weighed;  or,  for  a  small  engine,  the  oil 
may  be  drawn  from  a  calibrated  vessel  such  as  a  vertical  pipe. 

In  an  engine  using  an  igniting  flame  the  gas  or  oil  required  for 
it  should  be  included  in  that  of  the  main  supply,  but  the  amount 
so  used  should  be  stated  separately,  if  possible. 

IX.  Measurement  of  Heat-Units  Consumed  by  the  Engine.  — 
The  number  of  heat  units  used  is  found  by  multiplying  the  num- 
ber of  pounds  of  coal  or  oil  or  the  cubic  feet  of  gas  consumed,  by 
the  total  heat  of  combustion  of  the  fuel  as  determined  by  a  cal- 


494  INTERNAL  COMBUSTION  ENGINES 

orimeter  test.  In  determining  the  total  heat  of  combustion  no 
deduction  is  made  for  the  latent  heat  of  the  water  vapor  in  the 
products  of  combustion.  There  is  a  difference  of  opinion  on 
the  propriety  of  using  this  higher  heating  value,  and  for  purposes 
of  comparison  care  must  be  taken  to  note  whether  this  or  the 
lower  value  has  been  used.  The  calorimeter  recommended  for 
determining  the  heat  of  combustion  is  the  Mahler,  for  solid  fuels 
or  oil,  or  the  Junker  for  gases,  or  some  form  of  calorimeter  known 
to  be  equally  reliable.  (See  Chapter  VI,  or  Poole  on  "  The  Calorific 
Power  of  Fuels.") 

It  is  sometimes  desirable,  also,  to  have  a  complete  chemical 
analysis  of  the  oil  or  gas.  The  total  heat  of  combustion  may  be 
computed,  if  desired,  from  the  results  of  the  analysis,  and  should 
agree  well  with  the  calorimeter  values. 

In  using  the  gas  calorimeter,  which  involves  the  determina- 
tion of  the  volume  instead  of  the  weight  of  the  gas,  it  is  important 
that  this  should  be  reduced  to  the  same  temperature  as  that 
corresponding  to  the  conditions  of  the  engine  trial.  The  formula 
to  be  used  for  making  the  reduction  is  that  already  given  in 
Section  V  (d). 

For  the  purpose  of  making  the  calorimeter  test,  if  the  fuel 
used  is  coal  for  generating  gas  in  a  producer,  or  oil,  samples  should 
be  taken  at  the  time  of  the  engine  trial,  and  carefully  preserved 
for  subsequent  determination.  If  gas  is  used,  it  is  better  to  have 
a  gas  calorimeter  on  the  spot,  samples  taken,  and  the  calorimeter 
test  made  while  the  trial  is  going  on. 

X.  Measurement  of  Jacket  Water  to  Cylinder  or  Cylinders.  — 
The  jacket  water  may  be  measured  by  passing  it  through  a  water 
meter  or  allowing  it  to  flow  from  a  measuring  tank  before  enter- 
ing the  jacket,  or  by  collecting  it  in  tanks  on  its  discharge. 

XI.  Indicated  Horse-Power.  —  The  directions  given  for  deter- 
mining the  indicated  horse-power  for  steam  engines  apply  in  all 
respects  to  internal  combustion  engines. 

The  indicated  horse-power  should  be  determined  from  the 
average  mean  effective  pressure  of  diagrams  taken  at  intervals  of 
twenty  minutes,  and  at  more  frequent  intervals  if  the  nature  of 
the  test  makes  this  necessary.  With  variable  loads,  such  as  those 
of  engines  driving  generators  for  electric  railroad  work,  and  of 
rubber-grinding  and  rolling  mill  engines,  the  diagrams  cannot  be 


METHODS  OF  TESTING  GAS  ENGINES  495 

taken  too  often.  In  cases  like  the  latter,  one  method  of  obtain- 
ing suitable  averages  is  to  take  a  series  of  diagrams  on  the  same 
blank  card  without  unhooking  the  driving  cord,  and  apply  the 
pencil  at  successive  intervals  of  ten  seconds  until  two  minutes' 
time  or  more  has  elapsed,  thereby  obtaining  a  dozen  or  more 
indications  in  the  time  covered.  This  tends  to  insure  the  deter- 
mination of  a  fair  average  for  that  period.  In  taking  diagrams 
for  variable  loads,  as  indeed  for  any  load,  the  pencil  should  be 
applied  long  enough  to  cover  several  successive  revolutions,  so 
that  the  variations  produced  by  the  action  of  the  governor  may 
be  properly  recorded.  To  determine  whether  the  governor  is 
subject  to  what  is  called  "racing"  or  "hunting,"  a  "variation 
diagram"  should  be  obtained;  that  is,  one  in  which  the  pencil  is 
applied  a  sufficient  time  to  cover  a  complete  cycle  of  variations. 
When  the  governor  is  found  to  be  working  in  this  manner,  the 
defect  should  be  remedied  before  proceeding  with  the  test. 

AUTHOR'S  NOTE.  —  When  the  engine  is  governed  by  the  hit-and-miss 
principle  the  diagrams  taken  on  one  card  should  in  any  case  cover  the  series 
of  consecutive  explosions,  and  the  mean  diagram  should  be  used  as  the  basis 
of  calculations. 

The  most  satisfactory  driving  rig  for  indicating  seems  to  be 
some  form  of  well-made  pantagraph,  with  driving  cord  or  fine 
annealed  wire  leading  to  the  indicator.  The  reducing  motion, 
whatever  it  may  be,  and  the  connections  to  the  indicator,  should 
be  so  perfect  as  to  produce  diagrams  of  equal  lengths,  and  pro- 
duce a  proportionate  reduction  of  the  motion  of  the  piston  at 
every  point  of  the. stroke,  as  proved  by  test. 

To  test  the  accuracy  of  the  reducing  motion  without  making 
special  preparations  for  a  thorough  examination,  it  is  sufficient 
to  make  a  comparison  between  the  actual  proportion  of  the  stroke 
covered  and  the  apparent  proportion  measured  on  the  indicator, 
and  see  how  they  agree.  This  may  be  done  on  a  large  engine  by 
making  the  comparison  \vherever  it  happens  to  stop,  and  repeat- 
ing the  comparison  when  it  has  stopped  with  the  piston  at  some 
other  point  of  the  stroke.  With  an  engine  which  can  be  turned 
over  by  hand,  or  where  auxiliary  power  is  provided  for  moving 
it,  the  comparison  may  be  made  at  a  number  of  equidistant 
points  in  the  stroke.  To  make  the  test  properly,  a  diagram 
should  be  taken  just  before,  stopping,  and  this  will  serve  as  a 


496  INTERNAL  COMBUSTION  ENGINES 

reference  for  the  measurements  taken  after  stopping.  The  actual 
proportion  of  stroke  covered  is  determined  by  measuring  the 
distance  which  the  piston  has  moved  and  comparing  it  with  the 
whole  length  of  the  stroke,  making  sure  that  the  slack  has  all 
been  taken  up.  To  obtain  the  apparent  indication  from  the  dia- 
gram, the  indicator  pencil  is  moved  up  and  down  with  the  finger 
so  as  to  make  a  vertical  mark  on  the  diagram,  and  the  distance 
of  this  mark  from  the  beginning  of  the  diagram  compared  to  the 
whole  length  of  the  diagram  is  the  proportion  desired. 

It  is  necessary,  of  course,  to  go  through  these  operations  with- 
out changing  in  any  way  the  adjustment  of  the  driving  cord  of 
the  indicator,  or  any  part  of  the  mechanism  that  would  alter  the 
movements  of  the  indicator. 

In  the  manipulation  of  the  indicator  it  is  important  to  keep 
the  instrument  in  clean  condition  and  preserve  it  in  mechanically 
good  order.  Ordinary  cylinder  oil  is  the  best  material  to  use  for 
lubricating  the  indicator  piston  for  pressures  above  the  atmos- 
phere. It  is  better  to  have  the  piston  fit  the  cylinder  rather 
loosely  —  so  as  to  get  absolute  freedom  of  motion  —  than  to 
have  a  mechanically  accurate  fit.  In  the  latter  case,  extreme 
care  and  frequent  cleanings  are  required  to  obtain  good  diagrams. 
No  diagrams  should  be  accepted  in  which  there  is  any  appearance 
of  want  of  freedom  in  the  movement  of  the  mechanism.  A  ragged 
or  serrated  line  in  the  region  of  the  expansion  or  compression 
lines  is  a  sure  indication  that  the  piston  or  some  part  of  the 
mechanism  sticks;  and  when  this  state  of  things  is  revealed  the 
indicator  should  not  be  trusted,  but  the  cause  should  be  ascer- 
tained and  a  suitable  remedy  applied.  An  indicator  which  is 
free  when  subjected  to  a  steady  pressure,  as  it  is  under  a  test 
of  the  springs  for  calibration,  should  be  able  to  produce  the  same 
horizontal  line,  or  substantially  the  same,  after  pushing  the 
pencil  down  with  the  finger,  as  that  traced  after  pushing  the 
pencil  up  and  subsequently  tapping  it  lightly.  When  the  pencil 
is  moved  by  the  finger,  first  up  and  then  down,  the  piston  being 
subjected  to  the  pressure,  the  movement  should  appear  smooth 
to  the  sense  of  feeling. 

The  pipe  connections  for  indicating  gas  and  oil  engines  should 
be  removed  as  far  as  possible  from  the  ports  and  ignition  devices, 
and  made  preferably  in  the  cylinder  head.  The  pipes  should  be 


METHODS  OF  TESTING  GAS  ENGINES 


497 


as  short  and  direct  as  possible.  Avoid  the  use  of  long  pipes, 
otherwise  explosions  of  the  gas  in  these  connections  may  occur. 

Ordinary  indicators  suitable  for  indicating  steam  engines  are 
much  too  lightly  constructed  for  gas  and  oil  engines.  The  pencil 
mechanism,  especially  the  pencil  arm,  needs  to  be  very  strong  to 
prevent  injury  by  the  sudden  impact  at  the  instant  of  the  ex- 
plosion; a  special  gas-engine  indicator  is  required  for  satisfactory 
work,  with  a  small  piston  and  a  small  spring. 

See  Chapter  I  for  the  description  of  various  indicators. 

XII.  Brake  Horse-Power.  —  The  determination  of  the  brake 
horse-power,  which  is  very  desirable,  is  the  same  for  internal 
combustion  as  for  steam  engines. 

This  term  applies  to  the  power  delivered  from  the  fly-wheel 
shaft  to  the  engine.  It  is  the  power  absorbed  by  a  friction  brake 
applied  to  the  rim  of  the  wheel,  or  to  the  shaft.  A  form  of  brake 
is  preferred  that  is  self-adjusting  to  a  certain  extent,  so  that  it 
will,  of  itself,  tend  to  maintain  a  constant  resistance  at  the  rim 
of  the  wheel.  One  of 
the  simplest  brakes 
for  comparatively 
small  engines,  which 
may  be  made  to  em- 
body this  principle, 
consists  of  a  cotton 
or  hemp  rope,  or  a 
number  of  ropes,  en- 
circling the  wheel, 
arranged  with  weigh- 
ing scales  or  other 
means  for  showing 
the  strain.  Anordi-  FlG-  16~2' 

nary  band  brake  may  also  be  constructed  so  as  to  embody  the 
principle.  The  wheel  should  be  provided  with  interior  flanges 
for  holding  water  used  for  keeping  the  rim  cool. 

A  self-adjusting  rope  brake  is  illustrated  in  Fig.  16-2,  where 
it  will  be  seen  that,  if  the  friction  at  the  rim  of  the  wheel  increases, 
it  will  lift  the  weight  A,  which  action  will  diminsh  the  tension  in 
the  end  B  of  the  rope,  and  thus  prevent  a  further  increase  in  the 
friction.  The  same  device  can  be  used  for  a  band  brake  of  the 


498 


INTERNAL  COMBUSTION  ENGINES 


ordinary  construction.  Where  space  below  the  wheel  is  limited, 
a  cross  bar,  C,  supported  by  a  chain  tackle  exactly  at  its  center 
point,  may  be  used  as  shown  in  Fig.  16-2,  thereby  causing  the 
action  of  the  weight  on  the  brake  to  be  upward.  A  safety  stop 
should  be  used  with  either  form,  to  prevent  the  weights  being 
accidentally  raised  more  than  a  certain  amount. 

The  water-friction  brake  is  specially  adapted  for  high  speeds 
and  has  the  advantage  of  being  self-cooling.  The  Alden  brake  is 
also  self-cooling  and  is  capable  of  fine  adjustment. 

A  water-friction  brake  is  shown  in  Fig.  16-3.  It  consists  of 
two  circular  discs,  A  and  B,  attached  to  the  shaft  C,  and  revolv- 
ing in  a  case,  E,  be- 
tween fixed  planes. 
The  space  between 
the  discs  and  the 
planes  is  supplied 
with  running  water, 
which  enters  at  D 
and  escapes  at  the 
cocks  F,  G,  and  H. 
The  friction  of  the 
water  against  the 
surfaces  constitutes 
a  resistance  which 
absorbs  the  desired  power,  and  the  heat  generated  within  is 
carried  away  by  the  water  itself.  The  water  is  thrown  outward 
by  centrifugal  action  and  fills  the  outer  portion  of  the  case. 
The  greater  the  depth  of  the  ring  of  water,  the  greater  amount 
of  power  absorbed.  By  suitably  adjusting  the  amount  of  water 
entering  and  leaving  any  desired  power  can  be  obtained.  Water- 
friction  brakes  have  been  used  successfully  at  speeds  of  over 
20,000  revolutions  per  minute. 

For  methods  of  computing  brake  horse-power  see  Chapter  I. 
XIII.  Speed.  —  There  are  several  reliable  methods  of  ascer- 
taining the  speed,  or  the  number  of-  revolutions  of  the  engine 
crank  shaft  per  minute.  The  simplest  is  the  familiar  method  of 
counting  a  number  of  turns  for  a  period  of  one  minute  with  the 
eye  fixed  on  the  second  hand  of  a  time  piece.  Another  is  the  use 
of  a  counter  held  for  a  minute  or  a  number  of  minutes  against 


FIG.  16-3. 


METHODS  OF  TESTING  GAS  ENGINES 


499 


the  end  of  the  main  shaft.  Another  is  the  use  of  a  reliable  tach- 
ometer held  likewise  against  the  end  of  the  shaft.  The  most 
reliable  method,  and  the  one  we  recommend,  is  the  use  of  a 
continuous  recording  engine  register  or  counter,  taking  the  total 
reading  each  time  that  the  general  test  data  are  recorded,  and 
computing  the  revolutions  per  minute  corresponding  to  the 
difference  in  the  readings  of  the  instrument.  When  the  speed  is 
above  250  revolutions  per  minute,  it  is  almost  impossible  to  make 
a  satisfactory  counting  of  the  revolutions  without  the  use  of 
some  kind  of  mechanical  counter. 

The  determination  of  variation  of  speed  during  a  single  revo- 
lution, or  the  effect  of  the  fluctuation  due  to  sudden  changes  of 
the  load,  is  also  desirable,  es- 
pecially in  engines  driving  electric 
generators  used  for  lighting  pur- 
poses. There  is  at  present  no 
recognized  standard  method  of 
making  such  determinations,  and 
if  such  are  desired,  the  method 
employed  may  be  devised  by  the 
person  making  the  test  and  de- 
scribed in  detail  in  the  report. 

One  method  suggested  for 
determining  the  instantaneous 
variation  of  speed  which  accom- 
panies a  change  of  load  is  as 
follows:  A  screen  containing  a 
narrow  slot  is  placed  on  the  end 
of  a  bar  and  vibrated  by  means 
of  electricity.  A  corresponding 
slot  in  a  stationary  screen  is 
placed  parallel  and  nearly  touch- 


FIG.  16-4. 


ing  the  vibrating  screen,  and  the 
two  screens  are  placed  a  short 
distance  from  the  fly-wheel  of  the  engine  in  such  a  position  that 
the  observer  can  look  through  the  two  slots  in  the  direction  of  the 
spokes  of  the  wheel.  The  vibrations  are  adjusted  so  as  to  con- 
form to  the  frequency  with  which  the  spokes  of  the  wheel  pass 
the  slots. 


500  INTERNAL  COMBUSTION  ENGINES 

When  this  is  done  the  observer  viewing  the  wheel  through  the 
slots  sees  what  appears  to  be  a  stationary  fly-wheel.  When  a 
change  in  the  velocity  of  the  fly-wheel  occurs,  the  wheel  appears 
to  revolve  either  backward  or  forward  according  to  the  direction 
of  the  change.  By  careful  observations  of  the  amount  of  this 
motion,  the  change  of  angular  velocity  during  any  given  time  is 
revealed. 

Experiments  that  have  been  made  with  a  device  of  this  kind 
show  that  the  instantaneous  gain  of  velocity,  upon  suddenly 
removing  all  the  load  from  an  engine,  amounted  to  from  one- 
sixth  to  one-quarter  of  a  revolution  of  the  wheel. 

In  an  engine  which  is  governed  by  varying  the  number  of  ex- 
plosions or  working  cycles,  a  record  should  be  kept  of  the  number 
of  explosions  per  minute;  or  if  the  engine  is  running  at  nearly 
maximum  load,  by  counting  the  number  of  times  the  governor 
causes  a  miss  in  the  explosions. 

One  way  of  mechanically  recording  the  explosions  is  to  attach 
to  the  exhaust  pipe  a  cylinder  and  piston  arranged  so  that  the 
pressure  caused  by  the  exhaust  gases  operate  against  a  light 
spring  and  moves  a  register,  which,  is  provided  for  automatically 
counting  the  number. 

AUTHOR'S  NOTE.  —  An  instrument  for  this  purpose  has  been  devised  by 
R.  Mathot.  The  following  description  is  from  his  book  on  "  Modern  Gas 
Engines  and  Producer  Gas  Plants:'' 

The  instrument,  Fig.  16-4,  is  somewhat  similar  in  form  to  the  ordinary 
indicator.  Its  record,  however,  is  made  on  a  paper  tape  which  is  continuously 
.unwound.  The  cylinder  c  is  provided  with  a  piston  p,  about  the  stem  of 
which  a  spring  .s  is  coiled.  A  clock  train  contained  in  the  chamber  b  unwinds 
the  strip  of  paper  from  the  roll  p'  and  draws  it  over  the  drum  p",  where  the. 
pencil  t  leaves  the  mark.  The  tape  is  then  rewound  on  the  spindle  p'" ' .  A 
small  stylus  or  pencil  /  traces  the  atmospheric  line  on  the  paper  as  it  passes 
over  the  drum  p" '.  In  order  to  obviate  the  binding  of  the  piston  p  when 
subjected  to  the  high  temperature  of  the  explosions,  the  cylinder  c  is  provided 
with  a  casing  e  in  which  water  is  circulated  by  means  of  a  small  rubber  tube 
which  fits  over  the  nipple  e' '.  This  recorder  analyzes  with  absolute  precision 
the  work  of  all  engines,  whatever  may  be  their  speed.  It  gives  a  continuous 
graphic  record  from  which  the  number  of  explosions,  together  with  the  initial 
pressure  of  each,  can  be  determined,  and  the  order  of  their  succession.  Con- 
sequently the  regularity  or  irregularity  of  the  variations  can  be  observed 
and  traced  to  the  secondary  influences  producing  them,  such  as  the  action 
of  the  inlet  and  outlet  valves  and  the  sensiti\>eness  of  the  governor.  It  renders 
it  possible  to  estimate  the  resistance  to  suction  and  the  back  pressure  due  to 
expelling  the  burnt  gases,  the  chief  causes  of  loss  in  efficiency  in  high-speed 
engines.  Furthermore,  the  influence  of  compression  is  markedly  shown 
from  the  diagram  obtained. 

The  recorder  is  mounted  on  the  engine;  its  piston  is  driven  back  by  each 
of  the  explosions  to  a  height  corresponding  with  their  force;  and  the  stylus 


METHODS  OF   TESTING  GAS  ENGINES  501 

or  pencil  controlled  by  the  lever  t  records  them  side  by  side  on  the  moving 
strip  of  paper.  The  speed  with  which  this  strip  is  unwound  conforms  with  the 
number  of  revolutions  of  the  engine  to  be  tested,  so  that  the  records  of  the 
explosions  are  placed  side  by  side  clearly  and  legibly. 

Their  succession  indicates  not  only  the  number  of  explosions  and  of 
revolutions  which  occur  in  a  given  time,  but  also  their  regularity,  the  num- 
ber of  misfires.  The  pressure  of  the  explosions  is  measured  by  a  scale  con- 
nected with  the  recorder-spring.  By  employing  a  very  weak  spring  which 
flexes  at  the  bottom  simply  by  the  effect  of  the  compression  in  the  engine 
cylinder,  it  is  possible  to  ascertain  the  amount  of  the  resistance  to  suction 
and  to  the  exhaust.  It  is  simply  sufficient  to  compare  the  explosion  record 
with  the  atmospheric  line,  traced  by  the  stylus  /.  By  means  of  this  appa- 
ratus, and  of  the  records  which  it  furnishes,  it  is  possible  analytically  to  regulate 
the  work  of  an  engine,  to  ascertain  the  proportion  of  air,  gas,  or  hydro- 
carbon which  produces  the  most  powerful  explosion,  to  regulate  the  com- 
pression, the  speed,  the  time  of  ignition,  the  temperature,  and  the  like. 

XIV.  Recording   the    Data.  —  The   time  of  taking  weights 
and  every  observation  should  be  recorded,  and  note  made  of 
every  event,   however   unimportant   it   may   seem   to   be.     The 
pressures,    temperatures,    meter    readings,    speeds,    and    other 
measurements  should  be  observed  every  20  or  30  minutes  when 
the   conditions   are   practically  uniform,   and   at   more   frequent 
intervals  if  they  are  variable.     Observations  of  the  gas  or  oil 
measurements  should  be  taken  with  special  care  at  the  expira- 
tion of  each  hour,  so  as  to  divide  the  test  into  hourly  periods,  and 
reveal  the  uniformity,  or  otherwise,  of  the  conditions  and  results 
as  the  test  goes  forward. 

All  data  and  observations  should  be  kept  on  suitable  prepared 
blank  sheets  or  in  notebooks. 

XV.  Uniformity  of  Conditions.  —  When  the  object   of  the 
test  is  to  determine  the  maximum  economy,  all  the  conditions 
relating  to  the  operation  of  the  engine  should  be  maintained  as 
constant  as  possible  during  the  trial. 

XVI.  Indicator    Diagrams    and     their    Analysis.  —  SAMPLE 
DIAGRAMS:    Sample   diagrams   nearest   to   the   mean   should   be 
selected  from  those  taken  during  the  trial  and  appended  to  the 
tables  of  the  results.     If  there  are  separate  compression  or  feed 
cylinders,   the   indicator  diagrams   from  these  should   be  taken 
and  the  power  deducted  from  that  of  the  main  cylinder. 

XVII.  Standards  of  Economy  and  Efficiency.  —  The  hourly 
consumption  of  heat,  determined  as  pointed  out  in  Article  IX, 
divided  by  the  indicated  or  the  brake  horse-power,  is  the  standard 
expression  of  engine  economy  recommended. 

In   making   comparisons   between  the  standard   for  internal 


502  INTERNAL  COMBUSTION  ENGINES 

combustion  engines  and  that  for  steam,  it  must  be  borne  in  mind 
that  the  former  relates  to  energy  concerned  in  the  generation  of 
the  force  employed,  whereas  in  the  steam  engine  it  does  not 
relate  to  the  entire  energy  expended  during  the  process  of  com- 
bustion in  the  steam  boiler.  The  steam  engine  standard  does 
not  cover  the  losses  due  to  combustion,  while  the  internal  com- 
bustion engine  standard,  in  cases  where  a  crude  fuel  such  as  oil 
is  burned  in  the  cylinder,  does  cover  these  losses.  To  make  a 
direct  comparison  between  the  two  classes  of  engines  considered 
as  complete  plants  for  the  production  of  power,  the  losses  in 
generating  the  working  agent  must  be  taken  into  account  in  both 
cases  and  the  comparison  must  be  on  the  basis  of  the  fuel  used: 
and  not  only  this,  but  on  the  basis  of  the  same  or  equivalent  fuel 
used  in  each  case.  In  such  a  comparison,  where  producer  gas 
is  used,  and  the  producer  is  included  in  the  plant,  the  fuel  con- 
sumption, which  will  be  the  weight  of  coal  in  both  cases,  may  be 
directly  compared. 

The  thermal  efficiency  ratio  per  indicated  horse-power  or  per 
brake  horse-power  for  internal  combustion  engines  is  obtained 
in  the  same  manner  as  for  steam  engines,  and  is  expressed  by  the 

fraction 

2545 

B.T.U.  per  H.P.  per  hour 

XVIII.  Heat  Balance.  —  For  purposes  of  scientific  research, 
a  heat  balance  should  be  drawn  which  shows  the  manner  in  which 
the  total  heat  of  combustion  is  expended  in  the  various  processes 
concerned  in  the  working  of  the  engine.  It  may  be  divided  into 
three  parts:  first,  the  heat  which  is  converted  into  the  indicated 
or  brake  work;  second,  the  heat  rejected  in  the  cooling  water  of 
the  jackets;  and  third,  the  heat  rejected  in  the  exhaust  gases, 
together  with  that  lost  through  incomplete  combustion  and 
radiation. 

To  determine  the  first  item,  the  number  of  foot-pounds  of  work 
performed  by,  say,  one  pound  or  one  cubic  foot  of  the  fuel  is 
determined;  and  this  quantity  divided  by  778,  which  is  the  me- 
chanical equivalent  of  one  British  thermal  unit,  gives  the  number 
of  heat  units  desired.  The  second  item  is  determined  by  meas- 
uring the  amount  of  cooling  water  passed  through  the  jackets, 
equivalent  to  one  pound  or  one  cubic  foot  of  fuel  consumed,  and 


METHODS  Of  TESTING  GAS  ENGINES  503 

calculating  the  amount  of  heat  rejected,  by  multiplying  this 
quantity  by  the  difference  in  the  sensible  heat  of  the  water  leav- 
ing the  jacket  and  that  entering.  The  third  item  is  obtained  by 
the  method  of  differences;  that  is,  by  subtracting  the  sum  of  the 
first  two  items  from  the  total  heat  supplied.  The  third  item  can 
be  subdivided  by  computing  the  heat  rejected  in  the  exhaust 
gases  as  a  separate  quantity.  The  data  for  this  computation 
are  found  by  analyzing  the  fuel  and  the  exhaust  gases,  or  by 
measuring  the  quantity  of  air  admitted  to  the  cylinder  in  addi- 
tion to  that  of  the  gas  or  oil. 

For  methods  of  making  fuel  and  exhaust  gas  computations, 
see  Chapter  VI. 

XIX.  Report  of  Test.  —  The  data  and  results  of  a  test  should 
be  reported  in  the  manner  outlined  in  one  of  the  following  tables, 
the  first  of  which  gives  a  complete  summary  when  all  the  data  are 
determined,  and  the  second  is  a  shorter  form  of  report  in  which 
some  of  the  minor  items  are  omitted. 

XX.  Temperatures  Computed  at  Various  Points  of  the  In- 
dicator Diagram.  —  The  computation  of  temperatures  correspond- 
ing to  various  points  in  the  indicator  is,  at  best,  approximate. 
It  is  possible  only  where  the  temperature  of  one  point  is  known 
or  assumed,  cr  where  the  amount  of  air  entering  the  cylinder 
along  with  the  charges  of  gas  or  oil,  and  the  temperature  of  the 
exhaust  gases,  is  determined. 

If  the  amount  of  air  is  determined  for  a  gas  engine,  together 
with  the  necessary  temperatures,  so  that  the  volume  and  the 
temperature  of  the  air  entering  the  cylinder  per  stroke,  and  that 
of  the  gas  are  known,  we  may,  by  combining  this  with  the  other 
data,  compute  the  temperature  for  a  point  in  the  compression 
curve.  In  this  computation  we  must  allow  for  the  volume  of 
the  exhaust  gases  remaining  in  the  cylinder  at  the  end  of  the 
stroke.  The  temperature  at  the  point  in  the  compression  curve 
where  it  meets  or  crosses  the  atmospheric  line  will  be  given  by 
the  formula: 


where  V  is  the  total  volume  corresponding  to  the  point  where 
the  compression  curve  meets  or  crosses  the  atmospheric  line;  V 


504  INTERNAL  COMBUSTION  ENGINES 

the  volume  of  the  air  at  atmospheric  pressure  entering  the  cylin- 
der during  each  working  cycle,  reduced  to  the  equivalent  volume 
at  32  degrees  Fahrenheit;  V"  the  volunie  of  the  gas  consumed 
per  cycle  reduced  to  the  equivalent  at  atmospheric  pressure  and 
32  degrees  Fahrenheit;  and  V""  the  volume  of  the  exhaust 
gases  retained  in  the  cylinder  reduced  to  the  same  basis.  To 
reduce  the  actual  volumes  to  those  at  32  degrees  Fahrenheit, 
multiply  by  the  ratios  of  491.4-  (T'  +  459.4),  where  T'  is  the 
observed  temperature  of  the  air  and  of  the  gas  used  as  fuel.  For 
the  exhaust  gases  retained  in  the  cylinder  at  the  end  of  the  stroke 
T'  may  be  taken  as  the  temperature  of  the  exhaust  gases  leaving 
the  engine,  provided  the  engine  is  not  of  the  "scavenging"  type. 
Having  determined  the  temperature  of  a  point  in  the  com- 
pression curve,  the  temperature  of  any  point  in  the  diagram  may 
be  found  by  the  equation 

7\  =  (T  +  459.4)  ^^i  -  459.4. . .  .(B). 

Here  7\  is  the  desired  temperature  of  any  point  in  the  diagram 
where  the  absolute  pressure  is  Pl  and  the  total  volume  Vlf  and 
P  and  V  are  the  corresponding  quantities  for  the  point  in  the 
compression  line  having  the  temperature  T  computed  from  the 
formula  (A). 

Formula  (B)  holds  only  where  the  weight  of  the  gases  contained 
in  the  cylinder  is  constant.  It  is  also  assumed  in  this  formula 
that  the  density  of  the  gas  compared  to  air  at  the  same  tempera- 
ture and  pressure  is  the  same  before  and  after  the  explosion. 

A  second  method  may  be  employed,  provided  the  air  which 
enters  the  cylinder  is  measured.  This  will  allow  for  any  dif- 
ference in  the  density  of  the  gas  before  and  after  explosion,  and 
more  exact  values  for  temperatures  on  the  expansion  curve  may 
be  obtained  than  by  the  first  method. 

In  this  method  the  density  of  the  exhaust  gases  compared  to 
air  at  the  same  temperature  and  pressure  is  computed,  assuming 
perfect  combustion,  and  including  the  effect  of  the  water  vapor 
present;  and  from  this  density  the  volume  of  the  gases  exhausted 
per  cycle  is  determined.  .  If  this  volume  exhausted  per  cycle, 
added  to  the  volume  of  the  gas  retained  in  the  clearance  space 
at  the  end  of  the  stroke,  be  called  V  in  equation  B,  and  T  be  the 


METHODS  OF  TESTING  GAS  ENGINES  505 

observed  temperature  of  the  exhaust  gases,  this  equation  may 
be  used  for  determining  the  temperature  of  any  point  in  the  dia- 
gram in  the  way  already  described.  This  method  is  more  com- 
plicated than  the  first,  as  it  involves  the  determination  of  the 
theoretical  density  after  explosion,  but  it  possesses  the  advantage 
that  it  may  be  applied  to  an  oil  as  well  as  to  a  gas  engine. 

A  third  method  of  computing  the  temperature  of  the  various 
points  in  the  diagram  may  be  employed  where  analyses  of  the 
exhaust  gases  as  well  as  of  the  fuel  have  to  be  made.  This  method 
is  more  complicated  than  the  first,  but,  in  common  with  the 
second,  it  possesses  the  advantage  that  it  may  be  applied  to  an 
oil  as  well  as  to  a  gas  engine. 

In  applying  the  third  method  the  volume  of  the  exhaust  gases 
discharged  per  working  cycle  would  be  given  by  the  formula: 


2 

where  D  is  the  density  of  the  exhaust  gases  at  their  observed 
temperature,  computed  from  the  analysis,  assuming  the  vapor 
of  water  produced  through  burning  the  hydrogen  in  the  fuel  to 
be  in  a  gaseous  state;  R  the  weight  of  the  air  which  enters  the 
cylinder  per  pound  of  fuel  consumed  per  working  cycle;  the  value 
of  R,  providing  there  are  no  unconsumed  hydrocarbons,  may  be 
computed  by  employing  the  formula: 

7?  -  NC 

.33(C02  +  CO)" 

where  N,  CO2  and  CO  represent  the  proportions,  by  volume,  of 
the  several  constituents  of  the  exhaust  gases,  and  C  the  weight 
of  carbon  consumed  and  converted  to  CO2  or  CO  per  pound  of 
fuel  burned,  computed  from  the  analysis  of  the  fuel  and  of  the 
exhaust  gases. 

Having  determined  the  volume  V2  of  the  exhaust  gases, 
formula  (B)  may  be  used  in  computing  the  temperature,  in  which 
case  T  will  represent  the  temperature  of  the  exhaust  gases  as  in  the 
second  method,  P  the  pressure  of  the  exhaust,  and  V  the  volume 
of  the  exhaust  gases  V2  discharged  per  stroke,  added  to  the  volume 
of  the  gases  retained  in  the  cylinder  at  the  end  of  the  stroke. 

The   value  of  R  given  in  equation   (D)  is  approximate,  on 


506  INTERNAL  COMBUSTION  ENGINES 

account  of  the  fact  that  the  percentage  of  N  should  be  that  due 
to  the  air  alone,  and  not  that  due  to  the  air  in  addition  to  that 
contained  in  the  fuel  gas.  Where  extreme  accuracy  is  desired, 
the  value  found  for  R  may  be  used  to  determine  the  percentage 
of  N  which  in  the  analysis  of  the  exhaust  gases  is  due  to  the  N 
in  the  fuel  gas,  and  this  value  may  be  subtracted  from  the  total 
N  shown  by  the  analysis  of  the  fuel  gases,  in  order  to  obtain  the 
correct  value  of  N  to  be  used  in  equation  (C). 

TABLE  NO.  1 
DATA  AND  RESULTS  OF  TEST  OF  GAS  OR  OIL  ENGINE 

Arranged  according;  to  the  Complete  Form  advised  by  the  Engine  Test  Com- 
mittee, American  Society  of  Mechanical  Engineers.     Code  of  1902 

1 .  Made  by of    

on  engine  located  at 

to  determine 

2.  Date  of  trial   

3.  Type  of  engine,  whether  oil  or  gas 


4.  Class  of  engine  (mill,  marine,  motor  for  vehicle,  pumping,  or  other)  ..... 

5.  Number  of  revolutions  for  one  cycle,  and  class  of  cycle  ........  ........ 

6.  Method  of  ignition  ............................................  ... 

7.  Name  of  builders  ................................................. 

8.  Gas  or  oil  used  ................................................... 

(a)  Specific  gravity  ...............................         deg.  Fahr. 

(6)  Burning  point    ................................ 

(c)  Flashing  point  .  .  ...............................  " 

9.  Dimensions  of  engine  : 

1st  Cyl.  •       2d  Cyl. 

(a)  Class  of  cylinder  (working  or  for  compressing 
the  charge)  .............................. 

(6)  Vertical  or  horizontal  .....  ...............  t 

(c)  Single  or  double  acting  ...................  . 

(d)  Cylinder  dimensions  ....................... 

Bore    ................................   in. 

Stroke     .............................  .   ft. 

Diameter  piston  rod    .................  .  .  in. 

Diameter  tail  rod   ......................  in. 

(e)  Compression  space  or  clearance  in  per  cent  of 

volume  displaced  by  piston  per  stroke.  . 
Head  end  .............................. 

Crank  end  ............................. 

•Average    ............  .  ................. 

(/)  Surface  in  square  feet  (average)   .......  ..... 

Barrel  of  cylinders    ..................... 


Cylinder  heads 
Clearance  and  ports 
Ends  of  piston 
Piston  rod    ..... 


METHODS  OF  TESTING  GAS  ENGINES  507 

(g)  Jacket  surfaces  or  internal  surfaces  of  cylinder 
heated  by  jackets,  in  square  feet  

Barrel  of  cylinder 

Cylinder  heads : 

Clearance  and  ports  

(h)  Horse-power  constant  for  one  Ib.  M.  E.  P.,  and 

one  revolution  per  minute 

10.  Give  description  of  main  features  of  engine  and  plant,  and  illustrate  with 

drawings  of  same  given  on  an  appended  sheet.  Describe  method  of 
governing.  State  whether  the  conditions  were  constant  throughout 
the  test. 

Total  Quantities 

11.  Duration  of  test  .  . hours. 

12.  Gas  or  oil  consumed    cu.  ft.  or  Ibs. 

13.  Air  supplied  in  cubic  feet  cubic  feet. 

14.  Cooling  water  supplied  to  jackets 

15.  Calorific  value  of  gas  or  oil  by  calorimeter  test,  determined 

by calorimeter    B.  T.  U. 

Hourly  Quantities 

16.  Gas  or  oil  consumed  per  hour    cu.  ft.  or  Ibs. 

17.  Cooling  water  supplied  per  hour Ibs. 

Pressures  and  Temperatures 

18.  Pressure  at  meter  (for  gas  engine)  in  inches  of  water ins. 

19.  Barometric  pressure  of  atmosphere: 

(a)  Reading  of  height  of  barometer 

(6)   Reading  of  temperature  of  barometer deg.  Fahr. 

(c)   Reading  of  barometer  corrected  to  32°  Fahr ins. 

20.  Temperature  of  cooling  water: 

(a)  Inlet    deg.  Fahr. 

(6)   Outlet   

21.  Temperature  of  gas  at  meter  (for  gas  engine) 

22.  Temperature  of  atmosphere: 

(a)  Dry-bulb  thermometer 

(6)  Wet-bulb  thermometer    

(c)    Degree  of  humidity per  cent. 

23.  Temperature  of  exhaust  gases  deg.  Fahr. 

How  determined 

Data  Relating  to  Heat  Measurement 

24.  Heat  units  consumed  per  hour  (Ibs.  of  oil  or  cu.  ft.  of  gas  per 

hour  multiplied  by  the  total  heat  of  combustion) B.  T.  U. 

25.  Heat  rejected  in  cooling  water: 

(a)  Total  per  hour 

(6)   In  per  cent  of  heat  of  combustion  of  the  gas  or  oil 

consumed  per  cent. 

26.  Sensible  heat  rejected  in  exhaust  gases  above  temperature 

of  inlet  air: 

(a)  Total  per  hour B.  T.  U. 

(6)  In  per  cent  of  heat  of  combustion  of  the  gas  or  oil  con- 
sumed        per  cent. 

27.  Heat  lost  through  incomplete  combustion  and  radiation 

per  hour: 

(a)  Total  per  hour B.  T.  U. 

(6)   In  per  cent  of  heat  of  combustion  of  the  gas  or  oil  con- 
sumed   ; , . . . .      per  cent. 


508  INTERNAL  COMBUSTION  ENGINES 

Speed,  Etc. 

28.  Revolutions  per  minute    • rev. 

29.  Average  number  of  explosions  per  minute 

How  determined 

30.  Variation  of  speed  between  no  load  and  full  load    rev. 

31.  Fluctuation  of  speed  on  changing  from  no  load  to  full  load 

measured  by  the  increase  in  the  revolutions  due  to  the 
change. 

Indicator  Diagrams 

1st  Cyl.         2d  Cyl. 

32.  Pressure  in  Ibs.  per  sq.  in.  above  atmosphere: 

(a)  Maximum  pressure  

(6)   Pressure  just  before  ignition 

(c)  Pressure  at  end  of  expansion    

(d)  Exhaust  pressure    

33.  Temperatures  in  deg.  Fahr.  computed  from  diagrams: 

(a)  Maximum    temperature    (not    necessarily    at 

maximum  pressure)    

(6)  Just  before  ignition 

(c)  At  end  of  expansion 

(d)  During  exhaust 

34.  Mean  effective  pressure  in  Ibs.  per  sq.  in 

Power 

35.  Power  as  rated  by  builders: 

(a)  Indicated  horse-power H.  P. 

(6)  Brake    

36.  Indicated  horse-power  actually  developed: 

First  cylinder   

Second  cylinder    " 

Total    

37.  Brake  H.  P.,  electric  H.  P.,  or  pump  H.  P.,  according  to  the 

class  of  engine    

38.  Friction  indicated  H.  P.  from  diagram,  with  no  load  on 
•     engine  and  computed  for  average  speed    

39.  Percentage  of  indicated  H.  P.  lost  in  friction  per  cent. 

Standard  Efficiency  Results 

40.  Heat  units  consumed  by  the  engine  per  hour: 

(a)  Per  indicated  horse-power B.  T.  U. 

(6)  Per  brake  horse-power 

41.  Heat  units  consumed  by  the  engine  per  minute: 

(a)  Per  indicated  horse-power " 

(6)   Per  brake  horse-power " 

42.  Thermal  efficiency  ratio: 

(a)  Per  indicated  horse-power per  cent. 

(6)  Per  brake  horse-power " 

Miscellaneous  Efficiency  Results 

43.  Cubic  feet  of  gas  or  Ibs.  of  oil  consumed  per  H.  P.  per  hour: 

(a)  Per  indicated  horse-power 

(6)  Per  brake  horse-power 

Heat  Balance 

44.  Quantities  given  in  per  cents  of  the  total  heat  of  combustion 

of  the  fuel: 


METHODS  OF  TESTING  GAS  ENGINES  509 

(a)  Heat  equivalent  of  indicated  horse-power    per  cent. 

(6)  Heat  rejected  in  cooling  water : 

(c)   Heat  rejected  in  exhaust  gases  and  lost  through  radia- 
tion and  incomplete  combustion    " 

Sum  =  100  " 

Subdivisions  o*f  Item  (c) : 

(cl)  Heat  rejected  in  exhaust  gases 

(c2)  Lost  through  incomplete  combustion    

(c3)  Lost  through  radiation,  and  unaccounted  for    ..... 

Sum  =  Item  (c) 

Additional  Data 

Add  any  additional  data  bearing  on  the  particular  objects  of  the  test  or 
relating  to  the  special  class  of  service  for  which  the  engine  is  to  be  used.  Also 
give  copies  of  indicator  diagrams  nearest  the  mean  and  the  corresponding 
scales.  Where  analyses  are  made  of  the  gas  or  oil  used  as  fuel,  or  of  the 
exhaust  gases,  the  results  may  be  given  in  a  separate  table. 

TABLE  NO.   2 
DATA  AND  RESULTS  OF  STANDARD  HEAT  TEST  OF  GAS  OR  OIL  ENGINE 

Arranged  according  to  the  Short  Form  advised  by  the  Engine  Test  Committee, 
American  Society  of  Mechanical  Engineers.     Code  of  1902. 


1 .   Made  by of 

on  engine  located  at    

to  determine  . 


2.  Date  of  trial    

3.  Type  and  class  of  engine 


4.  Kind  of  fuel  used 

(a)  Specific  gravity  deg.  Fahr. 

(6)   Burning  point    

(c)  Flashing  point 

5.  Dimensions  of  engine : 

IstCyl.     2dCyl. 
(a)  Class  of  cylinder  (working  or  for  compressing 

the  charge) 

(6)  Single  or  double  acting    

(c)  Cylinder  dimensions: 

Bore    in. 

Stroke ft. 

Diameter  piston  rod     in. 

(d)  Average  compression  space,  or  clearance  in  per 

cent 

(e)  Horse-power  constant  for  one  Ib.  M.  E.  P.  and 

one  revolution  per  minute 

Total  Quantities 

6.  Duration  of  test  hours. 

7.  Gas  or  oil  consumed    cu.  ft.  or  Ibs. 

8.  Cooling  water  supplied  to  jackets 

9.  Calorific  value  of  fuel  by  calorimeter  test,  determined  by 

. .  calorimeter   B.  T.  U. 


510  INTERNAL  COMBUSTION  ENGINES 

Pressures  and  Temperatures 

10.  Pressure  at  meter  (for  gas  engine)  in  inches  of  water ins. 

1 1 .  Barometric  pressure  of  atmosphere : 

(a)  Reading  of  barometer    

(6)  Reading  corrected  to  32  degs.  Fahr ! 

12.  Temperature  of  cooling  water: 

(a)  Inlet    deg.  Fahr. 

(6)  Outlet  

(c)   Degree  of  humidity    

13.  Temperature  of  gas  at  meter  (for  gas  engine) 

14.  Temperature  of  atmosphere: 

(a)  Dry  bulb  thermometer 

(6)  Wet  bulb  thermometer    

15.  Temperature  of  exhaust  gases 

Data  Relating  to  Heat  Measurement 

16.  Heat  units  consumed  per  hour  (pounds  of  oil  or  cubic  feet 

of  gas  per  hour  multiplied  by  the  total  heat  of  combus- 
tion) . B.T.U. 

17.  Heat  rejected  in  cooling  water  per  hour    

Speed,  Etc. 

18.  Revolutions  per  minute rev. 

19.  Average  number  of  explosions  per  minute    

Indicator  Diagrams 

20.  Pressure  in  Ibs.  per  sq.  in.  above  atmosphere: 

1st  Cyl.         2d  Cyl. 

(a)  Maximum  pressure 

(6)  Pressure  just  before  ignition 

(c)  Pressure  at  end  of  expansion    

(d)  Exhaust  pressure    

(e)  Mean  effective  pressure 

Power 

21.  Indicated  horse-power: 

First  cylinder   H.  P. 

Second  cylinder    " 

Total    

22.  Brake  horse-power " 

23.  Friction  horse-power  by  friction  diagrams    " 

24.  Percentage  of  indicated  horse-power  lost  in  friction per  cent. 

Standard  Efficiency,  and  Other  Results 

25.  Heat  units  consumed  by  the  engine  per  hour: 

(a)  Per  indicated  horse-power B.  T.  U. 

(5)  Per  brake  horse-power " 

26.  Pounds  of  oil  or  cubic  feet  of  gas  consumed  per  hour: 

(a)  Per  indicated  horse-power Ibs.  or  cu.  ft. 

(6)  Per  brake  horse-power  .  .  . " 

Additional  Data 

Add  any  additional  data  bearing  on  the  particular  objects  of  the  test  or 
relating  to  the  special  class  of  service  for  which  the  engine  is  to  be  used. 
Also  give  copies  of  indicator  diagrams  nearest  the  mean,  and  the  correspond- 
ing scales. 


METHODS  OF  TESTING  GAS  ENGINES  511 

RULES    FOR    TESTING    GAS     PRODUCERS    AND   GAS    ENGINES.        CODE 
OF   THE    GERMAN    SOCIETY    OF    ENGINEERS  * 

All  metric  units  have  been  transposed  to  English  units 

The  preparation  of  the  following  rules  for  making  gas  engine 
and  producer  tests  was  undertaken  by  a  committee  appointed 
from  the  Verein  deutscher  Ingenieure,  in  collaboration  with  the 
German  Society  of  Engine  Builders,  with  the  view  of  establishing 
definite  general  regulations  governing  such  tests.  It  is  desirable, 
by  specifying  the  important  proportions  of  the  examined  plants 
and  the  conditions  under  which  the  results  were  attained,  to  in- 
sure that  these  results  are  not  only  applicable  to  a  single  case, 
but  that  they  have  general  value.  To  attain  this  end  it  is  neces- 
sary that  all  data  should  be  given  uniformly  according  to  a  code 
of  regulations  such  as  that  here  presented. 

The  execution  of  such  tests  should  be  intrusted  only  to  per- 
sons possessing  the  required  expert  knowledge  and  practical 
experience.  These  persons  must  make  a  trial  plan,  or  schedule, 
appropriate  to  the  individual  case  in  hand,  which,  in  many  in- 
stances, will  not  require  that  all  of  the  investigations  stipulated 
in  the  general  code  are  actually  carried  out.  They  must  further 
examine  the  instruments  for  measuring  or  recording  purposes  as 
to  their  fitness  and  must  compile  the  results.  The  following 
rules,  the  adoption  or  selection  of  which  must  be  left  to  the 
soundness  of  judgment  of  the  investigator,  are  intended  to  serve 
as  a  basis  on  which  to  proceed. 

GENERAL    REGULATIONS 

Object  of  Investigation 

1.  The  object  of  a  test  made  on  a  producer-gas  plant  may  be 
to  determine : 

(a)  The  quantity,  composition,  and  calorific  value  of  the  fuel 
consumed. 

(&)  The  quantity,  composition,  and  heat  value  of  the  gas 
produced. 

(c)  The  degree  of  efficiency  of  the  producer-gas  plant. 

(d)  The  separate  heat  Igsses  in  the  plant. 

*  Mainly  from  F.  E.  Junge's  translation  in  Power,  Feb.,  1907. 


512  INTERNAL  COMBUSTION  ENGINES 

(e)  The  quantity  of  impurities  contained  in  one  cubic  meter 
or  one  cubic  foot  of  gas  (dust,  tar,  sulphur,  etc.). 

(/)  The  moisture  contents  of  the  gas. 

(g)  The  water  consumption  of  the  producer-gas  plant,  either 
total  or  in  the  separate  parts. 

(h)  The  mechanical  work  required  for  operating  the  plant, 
including  apparatus. 

(i)  The  duration  of  time  required  for  starting. 

(k)  The  stand-by  losses  during  intervals  of  shutting  down 
day  or  night. 

2.  The  object  of  a  test  made  on  an  internal  combustion  (gas) 
engine  may  be  to  determine: 

(a)  The  indicated  capacity  and  the  effective  output. 

(b)  The  mechanical  efficiency. 

(c)  The    fuel    consumption    and   the    heat    consumption    per 
horse-power  hour. 

(d)  The   consumption  of  lubricants,   separately   for  cylinder 
and  engine. 

(e)  The  consumption  of  water  and  the  heat  conducted  to  the 
cooling  water. 

(/)  The  fluctuations  in  number  of  revolutions. 
(g)  The  composition  of  exhaust  gases. 

NUMBER    AND  'DURATION    OF    TESTS 

Admissible  Fluctuations 

3.  The  number  and  duration  of  trials  are  determined  by  the 
purpose  of  the  test  as  well  as  by  a  consideration  of  the  conditions 
of  installation  and  operation,  and  must  be  settled  and  previously 
arranged  according  to  paragraphs  four  to  eight.     For  trials  of 
special  importance  the  results  of  which  are  decisive  for  acceptance 
tests,  for  penalties  or  for  premiums,  this  item  deserves  special 
consideration. 

4.  Acceptance  tests  should  be  made  if  possible  immediately 
after  a  plant  has  been  put  into  actual  operation;  the  manufacturers, 
however,  must  be  granted  a  reasonable  time  for  making  preliminary 
trials  of  their  own  and  for  carrying  out  alterations  or  improvements 
then  necessary.     The  length  of  this  time  and  other  conditions  are 
best  agreed  upon  when  drawing  up  the  delivery  contract. 


METHODS  OF  TESTING  GAS  ENGINES  513 

5.  In  order  to  be  able  to  get  acquainted  with  the  operation  of 
the  plant  that  is  to  be  tested,  to  find  time  for  examining  the 
testing  devices  employed,  and  to  break  in  observers  and  assistants, 
it  is  desirable  that  preliminary  trials  be  allowed. 

6.  If  the  fuel  consumption  in  gas  producers  is  to  be  deter- 
mined, the  trial  run  must  be  extended  over  at  least  eight  hours 
under  constant  conditions  and  without  interruptions. 

7.  For   determining   the   consumption   of   liquid   or  gaseous 
fuel  and  provided  the  conditions  are  constant,  it  is  sufficient  for 
the  higher  loads  to  extend  measurements  over  an  hour,  while  for 
finding  the  consumption  at   the  lower  loads,   measurements  of 
even  shorter  duration  are  sufficient.     To  ascertain  the  constancy 
of  the  conditions  the  temperature  of  the  outflowing  cooling  water 
must  be  read  from  time  to  time.     These  rules  as  to  the  duration 
of  the  tests  are  made  with  the  provision  that  no  interruption  or 
disturbance  of  the  trial  takes  place,  and  that  intermediate  read- 
ings show  only  slightly  varying  values  for  the  consumption. 

8.  If  only  the  mechanical  efficiency  of  an  engine  is  to  be 
determined,  trials  of  short   duration  under  constant  conditions 
are  sufficient;  but  at  least  ten  sets  of  indicator  cards  should  be 
taken. 

9.  For  investigations  of  special  importance  at  least  two  tests 
should  be  made,  one  after  the  other.     They  should  be  accepted 
only  if  no  interruptions  occurred  and  if  the  results  show  no  greater 
deviations  than  those  due  to  unavoidable  errors  of  observation. 
The  mean  of  the  two  results  is  to  be  taken  as  the  final  result. 

10.  The  extent  to  which  the  capacity  and  consumption  of 
gas  may  differ  from  the  guarantee  or  contract  figures,  without 
justifying  a  claim  of  breach  of  contract,  is  to  be  clearly  stated 
before  the  tests  (either  in  the  original  contract  or  in  the  schedule 
of  tests).     When  no  other  agreement  has  been  previously  arrived 
at,  the  capacity  guarantee  is  regarded  as   fulfilled  if  the  figure 
obtained  in  the  test   is   not   more    than   5   per  cent   below  the 
value  on  which  the  guarantee  was  based.     This  margin,  how- 
ever, is   allowable  only  for    the    maximum    output    which  was 
promised  beyond  the  guaranteed  continuous  output.     The  latter 
must  be  rendered  by  the  engine  under  all  circumstances. 

The  consumption  of  fuel  and  water  as  determined  on  test 
should  not  exceed  the  guaranteed  figures  by  more  than  5  per  cent 


514  INTERNAL  COMBUSTION  ENGINES 

even  if,  during  the  trial,  the  engine  load  fluctuated  somewhat 
from  the  load  upon  which  the  guarantee  was  based,  provided 
that  fluctuation  do  not  exceed  an  average  of  ±  5  per  cent  of  such 
load,  or  a  maximum  of  ±  15  per  cent. 

Since  it  is  often  impossible  when  making  .tests  to  have  the 
internal  combustion  engine  work  at  exactly  the  effective  (horse- 
power) capacity  on  which  the  guarantee  agreed  upon  in  the  con- 
tract is  based,  it  is  recommended  that  the  agreement  shall  specify 
the  expected  fuel  consumption  for  higher  and  lower  outputs. 
The  same  provision  is  perferably  made  also  with  gas  producers. 

UNITS    OF    MEASUREMENT   AND    DESIGNATIONS 

11.  When  giving  pressure  data  it  must  be  stated  whether 
absolute  pressures  or  gage    pressures    above    or  below  the   at- 
mospheric   are    meant.     Absolute    pressure    equals    atmospheric 
pressure  plus  gage  pressure. 

12.  All   temperature   and   heat    measurements    refer  to   the 
Fahrenheit  scale. 

13.  The  mechanical  equivalent  of  heat  is  taken  at  778  foot- 
pounds. 

14.  The  calorific  value  of  a  fuel  is  to  be  taken  as  its  lower 
heating  value;  that  is,  the  heat  which  is  liberated  by  the  com- 
plete combustion  of  the  fuel  when  the  burnt  products  are  cooled 
down  to  the  original  (room)  temperature  at  constant  pressure,  it 
being  assumed,  however,  that  the  water  of  combustion  and  the 
moisture  contained  in  the  fuel  remain  vaporized.     The  calorific 
value  must  be  based  on  the  unit   quantity  or  weight  of  original 
fuel,   without    deducting  ash,  moisture,  etc.,  and  is  to  be  ex- 
pressed in  heat  units.     For  both  solid  and  liquid  fuels  the  unit 
of  weight  is  the  pound. 

The  heat  value  of  gaseous  fuels  is  based  on  one  cubic  foot  at 
32  degrees  Fahrenheit,  and  760  millimeters  barometer  pressure, 
or  must  be  expressed  in  thermal  units  as  "effective"  heat  value, 
that  is,'  reduced  to  one  cubic  foot  of  actual  gas  used.  If  not 
specially  stated,  it  is  always  understood  that  the  heat  value 
recorded  is  that  of  gas  at  32  degrees  Fahrenheit  and  760  milli- 
meters barometer  pressure. 

In  this  country  the  general  standard  so  far  recommended 
seems  to  indicate  for  "standard  gas"  a  temperature  of  60  degrees 


METHODS  OF  TESTING  GAS  ENGINES  515 

Fahrenheit,  and  a  pressure  of  14.7  pounds  per  square  inch,  cor- 
responding to  the  usual  atmospheric  pressure. 

15.  The  efficiency  of  a  gas-producer  plant  is  the  ratio  of  the 
latent  heat  contained  in  the  gas  as  produced  to  the  heat  of  com- 
bustion of  the  total  weight  of  fuel  consumed  in  the  plant,  both 
items  being  computed  from  the  lower  heating   value.     In  pro- 
ducer-gas   plants   having   a  separately  fired  steam  boiler,  it   is 
advisable  also  to  determine  the  ratio  of  the  heat  which  is  chemi- 
cally bound  in  the  producer  gas  to  the  heat  equivalent  of  that 
portion  of  the  fuel  which  is  consumed  in  the  producer  proper  for 
making  such  gas. 

16.  The    unit    of    measurement    used    for    the     power    or 
work   output    of   an   internal   combustion  engine   is  the   horse- 
power  equal    to    33000    foot-pounds    per    minute.     It    must    be 
clearly    stated    whether    the    indicated    power,    or    the    useful 
or  available   power,   is   meant.     If   not   otherwise  designated  it 
is  understood  that  the  figures  refer  to  the  useful  or  available 
output. 

17.  The  indicated  power  of  the  engine,  or  the  indicated  work, 
isx  the  difference  between  the  total  power  developed  or  work  done, 
ana  the  indicated  power,  or  work,  which  is  consumed  within  the 
engine;  in  short,  the  difference   between  the   positive   and  the 
negative  indicated  power  or  work. 

AUTHOR'S  NOTE.  —  This  is  the  provision  which  caused  considerable  dis- 
cussion among  gas-engine  experts  some  time  ago.  It  means  as  it  stands,  that 
in  a  4-cycle  machine,  the  indicated  horse-power  is  that  determined  from  the 
work  diagram  minus  the  work  shown  by  the  lower  loop  diagram  ;  and,  in  a 
2-cycle  engine,  the  total  indicated  horse-power  as  determined  from  the  dia- 
gram of  the  power  cylinder  minus  the  pump  work  is  considered  as  the  indi- 
cated horse-power.  This  view  is  undoubtedly  correct  when  the  mechanical 
efficiency  of  the  engine  itself  as  a  machine  is  to  be  determined. 

The  power  required  at  "no  load"  is  the  power  indicated  when 
no  useful  work  is  rendered  by  the  engine. 

18.  Mechanical  efficiency  is  the  ratio  of  the  useful  power  to 
the  indicated  power  of  the  engine. 

19.  All  consumption  figures  should  be  reduced  to  the  hour 
basis,  and  if  they  are  to  be  compared  with  the  output  of  the 
engine  they   must   be  based  on  one  horse-power  hour.     If  not 
otherwise  agreed  upon,  these. data  refer  to  the  useful  or  available 
output  at  full  load. 


516  INTERNAL  COMBUSTION  ENGINES 

EXECUTION    OF   TESTS 

20.  If  the  quantity  of  gas  made  in  a  producer  or  the  weight 
of  fuel  consumed  in  an  engine  is  to  be  measured,  then  all  pipes  or 
ducts  which  are  not  used  in  the  test  must  be  cut  off  from  the  pip- 
ing which  leads  to  the  producer  and  engine  that  are  to  be  tested. 
This  is  best  done  by  means  of  blind  flanges.     The  active  ducts, 
pipes,  gas  holders,  etc.,  must  be  examined  with  regard  to  leakage 
and  made  tight  if  necessary.     Unavoidable  losses  due  to  leakage 
must  be  determined.     This  holds  especially  for  masonry  gas  mains. 

FUEL    CONSUMPTION    OF   A    GAS-PRODUCER    PLANT 

21.  The  kind,  number,  and  duration  of  tests  must  be  agreed 
upon  according  to  the  general  rules  laid   down  in   paragraphs   1 
to   10. 

22.  The  constructive  features  and  the  operative  conditions 
of  gas-producer  plants  must  be  described  and  illustrated  in  the 
report  by  drawings,  so  far  as  this  is  necessary,  to  arrive  at  a  clear 
understanding  of  the  manner  of  working  and  of  the  results  ob- 
tained. 

23.  Before  making  the  test  the  plant  should  be  examined  as 
to  whether  or  not  it  is  in  good  working  order. 

24.  The  quantity  of  fuel  consumed  in  the  gas  producer  is 
determined  by  taking  the  weight  of  the  fuel   which  is  charged 
into  the  producer  during  the  trials  in  order  that  the  producer  may 
contain  at  the  end  of  the  test  exactly  the  same  amount  of  heat  - 
either  liberated,  or  chemically  bound  in  the  fuel  —  that  it  con- 
tained when  starting  the  test.     To  meet  this  requirement  it  is 
not  sufficient  that  the  depth  of  the  fuel  bed  be  the  same  at  the 
end  as  it  was  at  the  beginning;  it  must  also  be  taken  into  con- 
sideration what  influence  the  ash  and  the  slag  left  in  the  pro- 
ducer, the  location  of  the  incandescent   zone,  the  formation  of 
fissures  and  cavities,  the  closeness  or  density  of  the  producer 
charge,  and  the  chemical  composition  of  the  burning  fuel  par- 
ticles exercise  on  the  heat  contents  of  the  producer. 

In  order  to  comply  with  this  requirement  the  following  rules 
should  be  followed: 

25.  When  starting  the    test    the    plant    should    be    in    the 
condition  of  stability  or  normal  working  condition,  if   possible. 


METHODS  OF  TESTING  GAS  ENGINES  517 

This  means  that  after  a  period  of  shut-down  for  cleaning  or 
repairs  it  should  be  in  active  operation  for  one  or  more  days, 
running  on  fuel  of  the  same  characteristics  and  size,  with  the 
same  depth  of  fuel  bed,  the  same  skill  of  attendance  as  regards 
the  charging  or  feeding  of  fresh  fuel  and  the  removing  of  slag, 
and  under  the  same  load  conditions  that  will  obtain  during  the 
test. 

26.  During  the  trial  the  producer  should  be  charged  and  poked 
as  nearly  in  accordance  with  the  requirements  for  attendance  as 
possible.     The  level  of  fuel  charged  must  be  the  same  at  the  be- 
ginning and  at  the  end  of  the  tests  and  should  be  kept  constant 
during  the  trial.     About  half  an  hour  before  starting  and  before 
stopping  a  test,  the  slag  and  ashes  should  be  removed. 

If  it  is  impossible  to  rake  out  the  ashes  during  the  operation  of 
the  producer,  the  plant  must  be  shut  down  immediately  after 
stopping  the  test,  the  ashes  must  be  taken  out  at  once  and  the 
producer  refilled  up  to  the  same  level  that  existed  when  starting 
the  test.  The  weight  of  fuel  used  for  this  purpose 'must  be  added 
to  the  consumption. 

27.  The  fuel   consumed  during  the  trial   must   be   weighed, 
also  the  fuel  which  has  not  been  burnt  and  remains  useful;  that 
is,  that  portion  which  drops  down  from  above  the  grate  while 
raking  out  the  ashes,  and  that  which  is  culled  out  from  the  ashes 
as  unburnt.     The  weight  of  the  former  may  be  deducted  from 
the  consumption,  but  not  the  amount  which  is  taken  out  from 
the  ashes,  nor  the  coal  dust  which  accumulates  in  the  scrubbers 
and  in  the  flues  between  the  producer  and  the  engine. 

28.  To  be  able  to  determine  the  quantity  of  ash  and  slag 
produced  during  the  trial,  the  ash  box  must  be  emptied  before 
the  test.     If  this  is  not  possible,  as  when  an  inclined  grate  is 
used,  the  refuse  in  the  ash  box  must  be  equalized  before  and  after 
the  run. 

29.  The  stand-by  losses  during    intervals  of  shutting  down 
at  day  and  night  must  be  determined. 

30.  In  order  to  get  a  representative  sample  of  the  solid  fuel, 
the  following  course  may  be  pursued:  Of  every  carload,  basket, 
or  other  measure  of  fuel,  put  a  shovelful  into  a  covered  receptacle. 
Immediately  after  the  test  is  over,  the  contents  of  the  receptacle 
should  be  broken,  mixed,  spread  and  quartered  by  drawing  the 


518  INTERNAL  COMBUSTION  ENGINES 

two  diagonals  of  a  square.  The  two  opposite  quarters  are  re- 
jected, the  two  others  broken  up  finer,  mixed  and  quartered, 
and  the  two  opposite  quarters  rejected.  This  is  continued  until 
a  sample  of  some  10  to  20  pounds  remains,  which  is  preserved, 
in  well-closed  receptacles,  for  analysis.  In  addition  to  this  a 
number  of  other  samples  must  be  put  away  in  air-tight  receptacles 
for  use  in  determining  the  contents  of  moisture  in  the  fuel. 

31.  The   composition   of   the    fuel   shall    be   determined    by 
chemical  analysis.     Its  contents  in  carbon  (C),  hydrogen  (H), 
oxygen  (O),  sulphur  (S),  ash  (A),  and  water  (W)  must  be  given 
in  percentage  of  weight  referred  to  the  original  fuel.     The  con- 
tents, in  the  fuel,  of  nitrogen  (N)  can  be  disregarded.     The  be- 
havior of  the  fuel  when  being  heated  should  be  determined  by 
a  coking  test. 

32.  The  calorific  value  of  the  fuel  must  be  determined  by 
calorimetric    analysis.     An    approximate    determination    of    the 
heating  value  can  be  made  on  the  basis  of  the  chemical  analysis 
by  employing  De  Long's  formula: 


Heating  value  =  145  C  +  522.3    H  -        +  40  S  -  9.66  W 
in  which  C,  0,  H,  S,  and  W  are  expressed  in  weight  per  cent. 

TESTING    AN    INTERNAL-COMBUSTION    ENGINE 

33.  Kind,  number,  and  duration  of  trials  to  be  agreed  upon 
according  to  the  general  regulations  Nos.  1  to  8. 

34.  The   constructive   features   and   operative   conditions   of 
the  engine  must  be  so  illustrated  in  the  report  as  to  enable  one 
to  form  a  correct  idea  of  the  manner  of  working  and  of  the  re- 
sults   of    operation.     Especially    important    are    the    type    and 
capacity  of  engine,  diameter  of  cylinder   and   piston-rod,  piston 
stroke,  contents  of  clearance  space,  and  other  essential  dimen- 
sions; the  normal  rate  of  revolution  and  the  admissible  fluctua- 
tions; kind  and  heat  value  of  fuel  for  which  the  engine  is  intended. 
The  diameter  of  the  cylinder  and  the  stroke  should  be  actually 
measured  if  this  is  possible. 

The  contents  of  the  compression  space  are  preferabty  deter- 
mined by  filling  with  water.  If  it  is  impossible  to  state  the 
cubical  contents  of  the  compression  space,  then  the  compression 


METHODS  OF  TESTING  GAS  ENGINES  519 

pressure  at  full  load  should  at  least  be  given.     This  is  done  by 
taking  an  indicator  card  while  the  ignition  is  interrupted. 

35.  Before   making  the  test  the  engine   must   be  examined 
internally  and  externally  as  to  whether  or  not  it  is  in  good  work- 
ing order. 

36.  The  number  of  revolutions  of  the  engine  should  be  deter- 
mined by  a  continuous  speed  counter,  the  records  of  which  must 
be  noted  at  certain  intervals,  and  must  be  checked  or  corrected 
from  time  to  time  by  direct  readings.     If  the  speed  conditions  of 
the  engine  are  to  be  investigated  it  is  essential  to  determine  the 
following  items: 

(a)  The  number  of  revolutions  under  constant  conditions  at 
maximum  load  and  at  no  load. 

(6)  The  fluctuations  in  speed  at  constant  load: 

(c)  The  temporary  change  in  the  number  of  turns  when  the 
load  is  suddenly  decreased  or  increased  from  a  given  constant 
load  by  a  prescribed  amount.  These  determinations  can  be 
executed  with  apparatus  of  the  character  of  the  Horn  tacho- 
graph. The  fluctuations  of  speed  during  the  performance  of  one 
engine  cycle  above  and  below  the  mean  value,  expressed  in  parts 
of  the  latter,  should  be  determined  by  calculation  unless  other- 
wise provided. 

The  coefficient  of  fly-wheel  regulation  is 


AT"  •  \ 

*• y  mm.  \ 
A'mm./ 


g  _  ^max.  -  JVmint  =  2  /ALax.  ~ 
*V  max.  H~.  -/Vmin.  \*V  max.  ~r 

2 

where  N  =  number  of  revolutions. 

37.  The  useful  output  can  be  determined  either  by  brake  test 
or  by  electrical  measurement. 

The  dimensions  and  weight  of  the  brake  should  be  determined 
before  the  trial. 

The  electrical  measurements  can  be  made  on  a  generator 
directly  coupled  to  the  gas  engine.  The  useful  work  is  com- 
puted from  the  output  of  the  dynamo.  The  efficiency  of  the  gen- 
erator should  be  determined  by  one  of  the  methods  as  laid  down 
in  the  "Rules  for  Judging  and  Testing  Electrical  Machinery  and 
Transformers/'  published  by 'the  association  of  German  electrical 
engineers.  If  the  efficiency  is  found  approximately  by  measuring 


520  INTERNAL  COMBUSTION  ENGINES 

the  determinable  losses,  then  an  adequate  amount  (say  2  per 
cent  of  the  full  load  output)  must  be  allowed  for  losses  not 
accounted  for. 

The  apparatus  with  which  the  electrical  measurements  are 
executed  must  be  calibrated  before  and  if  possible  also  after  the 
test. 

Whether  anything  besides  the  2  per  cent  above  allowed  should 
be  credited  to  the  gas  engine  for  increased  bearing  friction  and 
windage  of  the  generator  must  be  settled  in  each  individual 
case. 

Whether,  in  case  the  useful  output  can  neither  be  determined 
by  brake  test  or  by  electrical  measurements,  the  code  provision 
for  testing  steam  engines  can  be  admitted  as  correct  for  gas 
engines,  namely,  to  designate  the  useful  output  as  the  difference 
between  the  indicated  work  at  any  load  and  the  indicated 
work  at  no  load,  cannot  be  settled  at  the  present  state  of 
development,  since  results  of  accurate  investigations  are  not  yet 
available. 

38.  Indicators  must  be  connected  immediately  to  the  com- 
bustion   chamber    without    employing    long    piping    with    sharp 
bends,  and  one  indicator  must  be  provided  for  every  combustion 
chamber.     For   this   purpose   each   compression   chamber   must 
have  an  opening  for  three-quarter  or  one  inch  Whitworth  thread. 
The  same  holds  true  for  pump  cylinders. 

The  indicators  and  their  springs  must  be  calibrated  before  and 
after  the  test  according  to  the  accepted  standards. 

39.  During  the  test,  cards  should  be  taken  quite  frequently 
from  every  combustion  chamber  and  from  the  pump  cylinders. 
The  cards  should  be  designated  by  numbers,  and  the  time  when 
each  card  was  taken,  the  scale  of  springs  used  and  the  number 
of  single  cards  obtained  must  be  recorded  on  the  cards.     At  least 
five  diagrams  should  be  taken  on  one  card  successively.     From 
time  to  time  diagrams  indicated  with  a  weak  spring  should  be 
taken  from  the  combustion  chambers. 

The  indicated  work  at  no  load  should  be  determined  imme- 
diately after  stopping  the  main  test  and  while  the  engine  is  still 
warmed  up  ready  for  operation.  Care  must  be  taken  that  the 
no-load  cards  are  not  taken  during  an  acceleration  or  during  a 
retardation  period  of  the  fly-wheel. 


METHODS  OF  TESTING  GAS  ENGINES  521 

ANALYSIS  OF  THE  GAS  GENERATED  IN  A  PRODUCER-GAS  PLANT  OR 
CONSUMED  IN  AN  INTERNAL  COMBUSTION  ENGINE,  OR  OF  THE 
LIQUID  FUEL  USED 

40.  The  samples  for  the  chemical  analysis  of  the  gas  must  be 
taken  during  the  trial  at  regular  intervals  and  as  frequently  as 
possible. 

They  must  be  either  analyzed  on  the  spot  or  preserved  in 
glass  tubes  closed  by  melting  the  ends.  The  analysis  is  to  deter- 
mine, in  per  cent  of  volume,  the  contents  of  the  gas  in  carbon 
monoxide  (CO),  carbon  dioxide .  (CO2) ,  hydrogen  (H2),  marsh 
gas  (CH2),  heavy  hydrocarbons  and  oxygen  (O2). 

In  addition  it  is  recommended  to  determine  the  contents  of 
sulfur.  The  gas  samples  should  be  taken  from  the  gas  main 
between  the  cleaning  apparatus  and  the  engine. 

41.  The    heat    value    of   the   gas   should   be    determined   as 
often  as  possible  by  calorimetric  analysis,  and  the  burner  of  the 
calorimeter   should   be   fed   from   the   gas    main   without    inter- 
ruption.     In    suction    producer    plants    this    can    be    done    by 
means  of  a  gas  pump  drawing  from  the  main.     If  conditions 
should    make   it    necessary   that    a  sample   be   taken  'from  the 
pipe   while    the    calorimeter    is    shut    off,    such    sample    to   be 
later  transferred  to   and   burned   in   the   calorimeter,   then  the 
quantity  of  gas   so   taken  should   not   be   less   than  300   liters 
(10.59  cubic   feet),  in  order  that  the   calorimeter  may  at   first 
be  brought  into  the  condition  of  stability  as  regards  the  water 
of   combustion,    and    in   order    that    at    least    100   liters    (3.53 
cubic  feet)   remain  available  for  two  successive  analyses.     The 
suction  pump,  the  gas   holder   and   the   piping   must   be  made 
tight  with  special  care  when  making  a  calorimeter  analysis  of 
suction  gas. 

42.  The  gas  meter  of  the  calorimeter  in  which  the  heat  value 
of  the  gas  is  determined  must  be  calibrated.     For  determining 
the  temperatures  of  the  calorimeter  water,  only  thermometers 
with  calibration  certificates  or  others  compared  with  such  should 
be  used.     The  scales  must  be  divided  at  least  into  tenths  of  a 
degree. 

On  the  basis  of  the  chemical  analysis  the  heating  value  per 
standard  cubic  foot  of  gases  which  do  not  contain  heavy  hydro- 


522  INTERNAL  COMBUSTION  ENGINES 

carbons    can    be    computed  from    the    following    formula,  if  a 
calorimetric  analysis  cannot  be  made 

Heating   Value  =  3.42   CO  +  2.97   H2  +  9.52   CH4 

where  CO,  H2  and  CH4  are  expressed  in  volume  per  cent. 

43.  The  quantity  of  gas  produced  or  consumed  should  be 
measured  by  means  of  a  gas  holder  or  a  gas  meter.     The  cross- 
sectional  area  of  the  holder  should  be  determined  by  measure- 
ment of  its  circumference  at  several  places.     Consumption  tests 
with  the  gas  holder  shall  not  be  made  while  the  latter  is  exposed 
to  the"  sun. 

44.  The  gas  meter  must  be  calibrated  and  set  level ;  it  must  be 
so  filled  that  the  water  level  corresponds  to  the  normal  filling 
existing  during  calibration.       Between  the  gas  meter  and    the 
engine  a  pressure  regulator  must  be  installed  or  a  large  suction 
space  provided  so  that  the  water  level  shows  only  small  pulsations 
during  the  pressure  fluctuations. 

45.  At  intervals  corresponding  to  the  duration  of  test  the 
following  readings  should  be  taken:  position  of  the  bell  of  the 
gas  holder  at  three  places  or  the  records  shown  by  the  gas  meter; 
the  pressure  in  the  bell  or  in  the  gas  meter;  the  temperature  of 
the  gas  when  entering  and  when  leaving  the  gas  holder  or  the 
gas  meter  and  before  reaching  the  engine;  the  barometric  pressure. 

46.  If  the  temperature  of  the  gas  is  different  when  measuring 
the  consumption  than  when  measuring  the  heat  value,  the  com- 
putation must   also  take  into   account   the  increase  of  volume 
which  is  due  to  the  moisture  contents  of  the  gas  at  higher  tem- 
peratures. 

47.  The  consumption  of  liquid  fuel  must  be  determined  either 
by  weight  or  by  measuring  its  volume.     For  determining  heat 
value,  composition,  and  specific  weight  of  the  fuel  one  representa- 
tive average  sample  is  sufficient. 

48.  When  measuring  the  fuel  consumption  of  internal  com- 
bustion engines,  the  consumption  of  lubricating  oil  for  the  cylinder 
should  be  determined  at  the  same  time. 

49.  If  the  consumption  at  low  loads  of  a  double-acting  tan- 
dem or  twin  engine  is  to  be  determined,  it  is  not  allowable  to  shut 
off  the  gas  from  one  or  more  ends  of  the  cylinders,  provided  that 
no  other  arrangements  have  been  previously  agreed  upon  and 


METHODS  OF  TESTING  GAS  ENGINES  523 

are  mentioned  in  the  report,  or  that  the  governor  acts  automati- 
cally in  the  way  described. 

EXPLANATIONS    TO    VARIOUS    ARTICLES    OF   THE    CODE 

The  main  code  is  followed  by  a  number  of  explanations  from 
which  the  following  extracts  are  taken.  The  figures  refer  to  the 
paragraphs  of  the  above  code. 

1  &2 

In  most  cases  only  one  or  two  of  the  objects  of  test  mentioned 
are  taken  into  account  in  any  given  trial.  If  in  any  exceptional 
case  the  object  of  the  test  should  not  be  any  of  those  mentioned, 
it  should  be  a  simple  matter  to  adapt  the  rules  given. 

Under  2  (c)  the  term  horse-power  hour  is  used.  It  is  essential 
that  in  any  given  trial  this  term  be  more  closely  denned,  as  horse- 
power may  mean  indicated  brake,  or  even  horse-power  developed 
by  pumps. 

4 

It  is  extremely  desirable  that  the  contract  state  the  time 
allowed  the  manufacturer  for  adjustment  and  trial  runs,  because 
his  own  interests  may  make  him  call  sometimes  for  a  long, 
sometimes  for  a  short  period.  In  the  case  of  a  small  engine, 
more  or  less  a  commercial  stock  machine,  he  may  wish  to  have 
the  period  as  short  as  possible,  and  this  the  buyer  may  agree  to 
without  danger  of  loss  to  himself.  If,  however,  the  machine  is 
of  a  special  type,  or  one  provided  with  special  attachments,  it  is 
but  a  matter  of  justice  to  allow  the  manufacturer  a  reasonable 
time  in  which  to  break  in  the  engine  and  to  give  him  an  oppor- 
tunity to  correct  any  imperfections  that  may  appear.  It  is  to 
the  interest  of  the  buyer  to  grant  such  a  period  in  order  to 
become  familiar  with  the  machine  before  taking  over  the  entire 
responsibility  of  operating  it.  It  is  also  true  that  many  faults 
appear  only  after  some  weeks  of  operation. 

On  the  other  hand,  too  long  a  period  of  adjustment  is  in  many 
cases  not  acceptable  to  the  buyer,  because  any  extended  work  of 
improvement  usually  seriously  hampers  operation;  and  because 
in  many  cases  he  desires  an  operative  machine,  which  no  longer 
requires  the  care  of  the  manufacturer,  as  soon  as  possible. 

It  frequently  happens  that  no  acceptance  test  is  agreed  upon. 


524  INTERNAL  COMBUSTION  ENGINES 

In  such  cases  it  sometimes  happens  that  the  buyer  comes  back 
upon  the  manufacturer  for  faults  which  did  not  develop  until 
the  machine  had  been  in  operation  some  time. 

If  the  manufacturer  then  agrees  to  an  investigation  or  a  test, 
a  sufficient  period  should  be  given  him  to  make  any  investigation 
he  sees  fit  or  to  correct  any  imperfections  that  may  have  appeared 
before  the  decisive  trial  or  investigation  is  made.  This  sometimes 
leads  to  a  simple  settlement  of  the  matter  in  that  the  manufac- 
turer discovers  that  ignorance  or  carelessness  on  the  part  of  the 
operator  have  caused  the  imperfections  complained  of.  The 
granting  of  such  a  period  also  guards  the  buyer  against  any  later 
claim  of  the  manufacturer  that  during  the  trial  the  machine  was 
not  in  the  condition  in  which  he  delivered  it. 


Preliminary  tests  are  always  desirable,  but  not  absolutely 
necessary.  The  cost  of  any  kind  of  investigation  is  usually  quite 
high  and  of  course  the  cost  increases  directly  with  the  time. 
The  expert  called  will  therefore  make  such  tests  when  they  seem 
to  him  essential.  But  the  manufacturer  should  have  the  right 
to  call  for  the  time  necessary  for  such  trials  if  he  is  to  present 
the  machine  in  its  best  condition. 

6 

It  cannot  be  denied  that  eight  hours  is  a  rather  short  time, 
because  it  is  extremely  difficult  to  determine  whether  the  pro- 
ducer is  in  the  same  condition  at  the  end  as  at  the  beginning  of 
the  test,  and  because  this  uncertainty  may  lead  to  large  errors. 
On  the  other  hand  it  is  unquestionable  that  in  many  cases  a  longer 
time  would  call  forth  so  many  difficulties  in  operation  that  eight 
hours  would  seem  the  necessary  limit. 

The  rule  is  mainly  framed  to  prevent  trials  of  so  short  dura- 
tion that  serious  errors  can  hardly  be  avoided,  but  it  leaves  it 
to  the  judgment  of  the  experimenter  whether  to  make  the  tests 
longer  than  eight  hours  where  it  seems  desirable  and  is  possible 
to  do  so. 

7 

Intermediate  readings  are  recommended  without  qualification, 
since  they  form  the  best  criterion  of  the  constancy  of  conditions. 


METHODS  of  TESTING  GAS  ENGINES          525 

With  liquid  or  gas  fuels  of  constant  composition,  individual 
readings  every  five  minutes  apart  sometimes  show  no  variation 
for  hours  at  a  time.  In  such  a  case  it  is  useless  to  extend  the 
time  of  the  trial. 

8 

In  determining  the  mechanical  efficiency  of  an  engine  it  should 
not  be  forgotten  that,  although  the  average  load  may  be  con- 
stant, there  may  be  speed .  variations  due  to  the  inevitable  in- 
equality of  the  indicator  diagrams,  so  that  during  some  cycles  work 
is  done  in  accelerating  the  fly-wheel,  while  during  others  the  fly- 
wheel by  retardation  gives  up  some  of  its  kinetic  energy. 

To  minimize  any  error  ^  that  this  may  introduce  into  the 
determination  of  the  mechanical  efficiency,  at  least  ten  diagrams 
should  be  taken. 

If  the  conditions  are  otherwise  constant,  however,  it  is  not 
necessary  to  spread  these  diagrams  over  any  considerable  period 
of  time. 

It  is  self-evident  that  during  the  time  of  taking  the  diagrams 
the  supply  of  lubricating  oil  must  not  be  increased. 

Changes  in  the  mechanical  efficiency  of  the  engine,  as  for 
instance  those  due  to  fouling,  cannot  be  detected  with  certainty 
even  by  a  long  test  period;  they  become  noticeable  usually  only 
after  a  period  of  operation  extending  over  two  weeks.  The  de- 
termination of  the  mechanical  efficiency  of  an  engine,  after  con- 
stant conditions  of  operation  are  attained,  therefore  only  applies 
to  the  engine  in  its  then  existing  state  or  condition. 

The  number  of  diagrams  to  be  taken  on  one  card  cannot  be 
definitely  stated.  On  account  of  variation  in  the  diagrams, 
which  is  less  at  high  than  at  low  loads,  care  should  be  had  not  to 
take  too  few.  On  the  other  hand  it  is  useless  to  take  more  than 
can  be  clearly  distinguished.  The  running  together  of  a  larger 
number  of  diagrams  only  makes  their  evaluation  more  uncertain. 

10 

In  consideration  of  unavoidable  errors  of  observation,  possible 
errors  of  the  instruments  used,  etc.,  it  is  meet  and  usual  to  allow 
a  certain  margin  between  the  figures  found  on  trial  and  those 
guaranteed.  In  the  steam  engine  code  5  per  cent  is  allowed  for 
this,  and  it  seems  reasonable  to  assume  the  same  figure  in  this 


fctA  H 

OF  THE 

UNIVERSITY] 

OF 


526  INTERNAL  COMBUSTION  ENGINES 

case.  Only  in  one  point,  in  the  guaranteed  normal  capacity , 
does  the  gas  engine  call  for  an  exception. 

A  given  steam  engine  gives  its  most  economical  results  at  a 
certain  cut-off,  but  a  higher  capacity  can  always  be  obtained  at 
the  expense  of  a  little  economy,  that  is,  a  buyer  is  certain  that 
even  a  machine  slightly  too  small  will  give  him  sufficient  ca- 
pacity. A  gas  engine,  on  the  contrary,  works  with  the  greatest 
economy  at  its  maximum  load.  It  is  to  the  interest  of  the  buyer, 
therefore,  to  get  an  engine  exactly  suited  to  his  needs  and  not  to 
choose  it  too  large.  It  is  possible  for  the  same  reason  that  any 
engine,  if  lacking  slightly  in  guaranteed  capacity,  may  become 
absolutely  useless  to  the  buyer.  For  these  reasons  it  was  thought 
advisable  not  to  grant  the  manufacturer  any  leeway  whatever 
as  regards  guaranteed  capacity. 

It  is  clear,  therefore,  that  the  manufacturer  must  take  upon 
himself  any  possible  inaccuracies  in  the  measurements,  unless  he 
can  show  them  up  and  demand  a  new  trial.  For  that  reason  it  is 
well  for  him  to  make  his  guarantee  a  little  on  the  safe  side  of  what 
he  knows  his  engine  is  capable  of  developing.  On  the  other  hand, 
there  is  no  harm  done  to  the  interest  of  the  buyer  if  the  manu- 
facturer underrates  the  normal  capacity  of  his  machine,  because 
the  former  will  always  call  for  an  engine  of  a  certain  normal 
capacity  to  suit  his  needs.  If  he  fails  to  do  this,  but  places  his 
dependence  in  the  guaranteed  maximum -capacity,  he  is  open  to 
the  charge  of  carelessness. 

Since  during  acceptance  tests  it  is  often  not  possible  to  keep 
the  load  quite  constant,  it  became  necessary,  following  the  steam 
engine  code,  to  allow  a  certain  amount  of  variation,  within  which 
no  just  cause  could  be  found  for  objection  to  the  trial.  There 
are  cases  where  the  variations  occurring  are  much  greater,  as 
when  a  gas  engine  is  used  for  driving  a  roll  train.  But  no  one 
set  of  "Rules"  can  possibly  take  into  account  all  such  extreme 
cases,  and  in  such  instances  the  contract  should  contain  the 
necessary  agreements  to  make  any  test  clear  and  free  from  sub- 
sequent objections. 

The  wish  has  been  expressed  from  several  quarters,  that  the 
" Rules"  should  contain  a  definition  of  the  term  " Normal  Ca- 
pacity." On  account  of  the  peculiarity  of  the  gas  engine  above 
discussed  this  is  not  quite  feasible.  But  the  term  "Maximum 


METHODS  OF  TESTING  GAS  ENGINES  527 

Continuous  Capacity"  perhaps  defines  most  nearly  what  is  in- 
tended in  most  cases. 

14 

It  is  sometimes  the  case  that  the  heating  value  of  the  stand- 
ard cubic  foot,  that  is,  reduced  to  32  degrees  Fahrenheit  and 
760  mm.  barometer,  is  so  greatly  different  from  the  actual  value 
of  the  gas  as  used,  that  any  contract  which  contains  only  the 
heating  value  of  the  gas  stated  on  that  basis  does  not  convey 
much  meaning  to  the  non-technical  buyer.  If  for  instance  a 
given  gas  has  a  heating  value  of  135  B.  T.  U.  per  standard  cubic 
foot,  its  effective  heating  value  at  a  high  altitude  and  in  a  warm 
climate,  say  at  68  degrees  and  620  mm.  barometer,  will  only  be 
about  100  B.  T.  U.  per  cubic  foot.  To  obviate  any  misunder- 
standing, it  should  be  clearly  stated  that,  when  the  "effective" 
heating  value  of  the  gas  is  not  definitely  specified,  the  heating 
value  at  32  degrees  Fahrenheit  and  760  mm.  barometer  is  meant. 

19 

By  "full"  load  is  meant  the  normal  capacity,  as  per  para- 
graph 10. 

23 

For  acceptance  tests,  and  all  other  tests  which  are  intended 
to  decide  any  disagreements  between  manufacturer  and  buyer, 
such  examination  should  be  carried  out  in  the  presence  and  with 
the  aid  of  the  former,  as  already  mentioned  under  paragraph  4. 

24-26 

In  all  gas  producer  tests  it  is  hardly  possible  with  certainty  to 
have  all  conditions  exactly  the  same  at  the  end  as  at  the  begin- 
ning. But  since  any  difference  in  the  beginning  and  end  con- 
ditions may  lead  to  considerable  error,  which  can  only  be 
equalized  by  excessive  length  of  test,  the  "Rules"  are  intended 
to  operate  to  the  end  that  such  errors  are  not  in  any  way  magni- 
fied by  the  method  of  test.  Hence  the  detailed  statement  in  the 
regulations. 

27 

Since  in  actual  operation,  the  fuel  in  the  ash  or  the  coal  dust 
in  the  gas  mains  are  hardly  ever  utilized,  no  correction  should 


528  INTERNAL  COMBUSTION  ENGINES 

be  made  for  these  on  any  trial.  In  order,  however,  to  prevent 
the  results  from  being  influenced  by  insufficient  cleaning  of  the 
producer,  any  fuel  which  falls  out  from  above  the  grate  dur- 
ing the  cleaning  period  may  be  subtracted  from  the  amount 
charged. 

35 

See  explanation  under  23. 

37 

A  brake  test  of  a  large  engine  is  in  some  instances  not  possible, 
and  in  any  case  a  matter  of  considerable  cost.  In  many  cases, 
however,  the  larger  gas  engines  are  either  direct  connected  to  a 
generator  or  to  some  other  power  consumer,  as  a  blowing  cylinder. 
In  the  former  case  electrical  measurements,  from  which  the 
effective  horse-power  may  be  determined,  are  easily  made.  In  the 
latter  case  the  capacity  guarantee  will  in  most  instances  be  based 
upon  the  performance  of  the  power  consumer,  as  for  example 
the  air  compressed  by  the  blowing  cylinder.  Outside  of  engines 
of  this  type,  however;  thero  still  remain  many  cases  in  which  it 
would  be  of  the  utmost  value  to  have  some  means  of  determining 
the  effective  capacity,  and  it  should  not  be  forgotten  that,  even 
in  the  case  of  medium-sized  machines,  a  braking  of  the  engine  at 
the  place  of  erection  is  often,  on  account  of  local  restrictions,  very 
difficult.  The  problem  has  been  solved  for  steam  engines  by 
assuming,  that  the  difference  between  the  indicated  horse-power 
at  any  load  and  the  indicated  horse-power  at  no  load  is  the  effec- 
tive or  useful  horse-power.  It  is  quite  possible  that  in  many 
cases  this  is  not  quite  correct,  but  the  method  is  very  generally 
accepted  and  followed. 

On  account  of  the  great  overload  capacity  of  the  steam  engine, 
a  small  error  in  this  respect  does  not  mean  a  great  deal.  But  the 
case  of  the  gas  engine  is  quite  different.  The  data  on  hand  does 
not  warrant  the  application  of  the  same  method  to  the  gas  engine, 
and  the  consequences  of  an  erroneous  conclusion  are  much  more 
serious  on  account  of  the  lack  of  overload  capacity. 

For  these  reasons  one  is  compelled  in  some  cases  to  omit  the 
determination  of  the  effective  capacity  altogether  and  to  be  con- 
tent with  the  determination  of  the  indicated  power  only.  It  is 
recommended  in  such  cases  that  the  mechanical  efficiency  be  not 


METHODS  OP  TESTING  GAS  ENGINES  529 

assumed  too  high  and  that  any  guarantees  regarding  fuel,  etc., 
also  be  based  upon  the  indicated  horse-power. 

It  is  sometimes  possible  to  brake  an  engine  on  the  test  floor 
of  the  factory.  The  mechanical  efficiency  may  thus  be  previously 
determined  when  it  is  known  that  no  brake  test  can  be  made  in 
the  final  place  of  erection. 

39 

The  number  of  diagrams  to  be  taken  during  any  given  test 
cannot  be  definitely  specified.  Much  depends  upon  the  length 
of  test,  and  the  decision  may  be  left  to  the  judgment  of  the 
experimenter. 

It  is,  however,  always  recommended  that  a  bundle  of  diagrams, 
instead  of  only  one,  be  taken  on  every  card.  Thus  a  series  of 
diagrams  are  obtained,  while,  if  only  a  single  diagram  is  taken,  it 
is  possible  to  hit  upon  the  same  diagram  in  the  series  a  number 
of  times.  (See  under  extract  8.) 

The  work  of  fluid  friction,  that  is,  the  lower-loop  diagram, 
cannot  be  determined  with  certainty  from  the  full  indicator 
cards.  It  is  best  for  that  reason  to  ignore  the  loop  when  deter- 
mining the  positive  work  and  to  find  the  negative  work  from  special 
weak  spring  diagrams. 

48 

The  measurements  of  the  quantity  of  lubricating  oil  used  is  of 
importance  in  smaller  engines,  because  the  fuel  consumption  can 
be  favorably  influenced  by  a  copious  supply  of  the  lubricant. 

49 

If  under  low  loads,  only  one  end  of  the  cylinder  is  allowed  to 
work,  the  fuel  consumption  would  be  much  lower.  But  since 
this  is  not  generally  done  in  operation,  the  results  would  be 
erroneous.  If,  however,  the  governor  during  operation  shuts  off 
the  individual  cylinders  or  cylinder  ends,  as  the  load  drops,  this 
is  of  course  also  permissible  during  a  test. 


CHAPTER  XVII 

THE    PERFORMANCE    OF    GAS    ENGINES    AND    GAS    PRODUCERS 

1.  As  indicated  in  the  rules  for  testing,  the  very  great  ma- 
jority of  tests  of  engines  are  made  to  determine  capacity  and  fuel 
consumption.     In  some  special   cases,   as   with   engines   driving 
generators,   tests   are   also   sometimes   made   of  the   regulation. 
These  three  tests  together  take  care  of  what  may  be  termed  the 
commercial  side  of  testing.     All  other  tests  are  special  in  that 
they  are  not  often  executed  in  an  acceptance  test,  but  form  in 
most  cases  the  object  of  scientific  or  laboratory  investigation. 

Such  investigations  are  in  many  instances  very  valuable,  and 
have  served  to  throw  a  flood  of  light  on  the  somewhat  complex 
cylinder  actions  of  the  internal  combustion  engine.  It  was  thus 
found  that  the  temperature  of  the  cylinder  walls,  i.e.,  the  cooling 
water  conditions,  piston  speed,  ignition,  proportion  of  mixture, 
compression,  etc.,  all  had  a  more  or  less  marked  effect  upon 
engine  performance.  In  the  following  the  results  obtained  and 
the  conclusions  drawn  by  various  experimenters  concerning  the 
effect  of  these  various  factors  are  briefly  set  forth. 

The  main  bulk  of  this  work  has  been  done  by  Witz  in  France, 
Slaby  and  E.  Meyer  in  Germany,  and  Burstall  and  others  in  Eng- 
land. In  spite  of  the  fact  that  none  of  these  investigations  are 
open  to  serious  objection  on  the  score  of  inaccuracy,  the  con- 
clusions arrived  at  are  not  always  in  accord.  This  is  undoubtedly 
due  to  the  complexity  of  the  cylinder  actions,  and  the  inter- 
dependence of  the  various  factors  entering  the  problem. 

2.  Cooling  Water  Conditions  and  Piston  Speed.  —  It  is  rea- 
sonable to  suppose  that  the  higher  the  wall  temperature  of  the 
cylinder,  i.e.,  the  smaller  the  temperature   difference   between 
mixture    and    wall   and  the  greater  the   piston    speed,   cutting 
down  the  time  of  exposure,  the  smaller  the  loss  to  the  jacket. 

The  heat  thus  saved,  however,  may  go  in  two  directions:  either 

530 


PERFORMANCE  OF  GAS  ENGINES 


531 


a  greater  thermal  efficiency  is  shown,  resulting  in  greater  power 
developed  for  the  same  expenditure  of  heat,  or  the  heat  saved 
from  going  into  the  jacket  is  lost  in  the  exhaust. 

Witz,  upon  the  basis  of  his  experiments,  comes  to  the  former 
conclusion,  and  says  "  The  action  of  the  jacket  is  the  great  regu- 
lator of  combustion  phenomena."  He  summarizes  his  results  as 
follows : 

1.  The  efficiency  increases  with  the  piston  speed  and  with  the 
temperature  of  the  surrounding  walls. 

2.  The  combustion  of  explosive  mixtures  is  the  more  rapid 
the  greater  the  speed  of  expansion  and  the  hotter  the  cylinder 
walls. 

The  work  of  Slaby  and  of  Meyer,  however,  seems  to  contro- 
vert these  conclusions.  Some  of  Slaby's  tests  show  that  while 
the  gas  consumption  per  horse-power  hour  decreases  somewhat 
with  an  increase  in  the  piston  speed,  there  is  an  increase  in 
the  consumption  with  a  rise  of  jacket  water  temperature.  The 
following  table  of  figures,  quoted  by  Schottler  from  some  of  Meyer's 
tests,  illustrates  the  point  that  the  heat  saved  from  the  jacket 
by  higher  piston  speed  may  go  to  the  exhaust,  leaving  the  ther- 
mal return  practically  unaffected. 


Ratio  of 
Com- 

R. P.  M. 

MEAN 
EFFECT- 
IVE 
PRESSURE 

Ratio 

HEATING 
VALUE  OF 
CHARGE 

WORK 

DONE   BY 

1  B.T.U. 

EXHAUST 
TEMP. 

HEAT  DISTRIBUTION 

IN% 

pression 

No.  1 

sq.  inch 

B.T.U. 

Ft.  Lbs. 

F 

Work 

Jacket 
Water 

Exhaust 

2.67 

187 

54.3 

7.11 

18.5 

140 

1022 

18.0 

51.2 

30.8 

2.67 

247 

51.7 

7.35 

17.4 

141 

1137 

18.1 

45.6 

36.3 

4.32 

187 

69.3 

7.43 

17.0 

190 

867 

24.4 

53.8 

21.8 

4.32 

247 

65.2 

7.40 

16.8 

184 

992 

23.7 

49.5 

26.8 

In  tests  of  this  kind  there  are  one  or  two  simultaneous  actions, 
not  directly  under  control,  which  may  serve  to  modify  the  final 
result  and  account  in  a  measure  for  the  discrepancy  appearing 
in  the  results  above  discussed.  An  increase  in  the  temperature 
of  the  walls  or  an  increase  in  the  piston  speed  both  cause  a  de- 
crease in  the  charge  volume,  the  former  by  heating  the  incoming 
charge  and  decreasing  the  density  of  the  mixture,  the  latter  by 
increased  friction  loss  in  pipes  and  ports.  The  direct  result  of 


532  INTERNAL  COMBUSTION  ENGINES 

this  is  that  the  effect  of  the  action  of  the  cylinder  wall  upon  the 
leaner  charge  is  proportionately  greater.  Thus  the  beneficial 
effect  of  greater  piston  speed  may  be  partly  annulled  by  the 
relatively  stronger  action  of  the  walls.  Further  it  is  true  that  a 
smaller  charge  weight  means  a  lower  compression  pressure,  and 
the  comparatively  greater  admixture  of  burned  gases  at  high 
speeds  causes  a  less  rapid  combustion.  Both  of  these  actions 
tend  to  decrease  the  efficiency.  There  are  thus  several  antago- 
nistic actions,  and  the  final  result  is  consequently  in  many  cases 
quite  problematical. 

The  net  result  of  an  increase  in  the  cylinder  wall  temperature 
or  of  the  piston  speed,  or  both,  in  an  existing  machine,  is  cer- 
tainly a  decrease  of  maximum  capacity  for  reasons  already 
pointed  out.  Further,  the  effect  of  a  variation  in  the  temperature 
of  the  jacket  water,  while  perhaps  not  quite  so  marked  in  engines 
using  gas,  is  certainly  quite  noticeable  in  liquid  fuel  engines, 
especially  those  using  kerosene  or  alcohol.  It  is  quite  possible 
in  kerosene  engines,  by  running  the  jacket  too  cold,  to  increase 
the  oil  consumption  seriously  by  condensation  of  the  oil  vapor  on 
the  comparatively  cold  cylinder  surfaces.  The  same  holds  true  of 
alcohol.  Thus  hot  walls  are  in  such  cases  of  undoubted  benefit. 
The  limits  to  temperature  are,  of  course,  decrease  of  engine 
capacity  and  danger  of  pre-ignition. 

3.  Compression.  —  The  theoretical  effect  of  increasing  the 
compression,  and  the  commercial  limits  to  this  increase  have 
already  been  discussed  in  Chapter  III.  Much  of  the  increased 
efficiency  of  blast  furnace  and  producer  gas  engines  as  compared 
with  illuminating  gas  and  liquid  fuel  engines  is  directly  due  to 
the  greater  compressions  that  the  former  fuels  can  stand.  The 
above  table  of  Meyer's  results  gives  some  idea  of  the  gain  that 
can  be  made  with  illuminating  gas  by  increasing  the  compression. 
With  a  compression  ratio  of  2.67,  the  average  thermal  efficiency 
was  18.05  per  cent,  with  a  ratio  of  4.32  the  average  was  24.05  per 

.      £  24.05  -  18.05 
cent,  a  gain  of  -   -  -  =  33  per  cent. 

lo.Uo 

Another  test  made  by  E.  Meyer  *  on  a  10  horse-power  engine, 
which  was  operated  with  illuminating  and  with  producer  gas, 
gave  the  following  results: 

*  E.  Meyer,  Z.  d.  V.  d.  I.,  July  5,  1902. 


PERFORMANCE  OF  GAS  ENGINES 


533 


INDICATED  THERMAL  EFFICIENCY 

COMPRESSION  RATIO 

With  Illuminating  Gas 

With  Producer  Gas 

4.98 

27.1 

24.4 

4.59 

26.5 

23.2 

3.84 

24.8 

21.5 

Here  again  the  beneficial  influence  of  the  higher  compression 
is  marked,  although  the  gain  is  not  so  great  as  in  the  former  case, 
owing  to  the  smaller  change  in  the  compression  ratio. 

Other  instances  pointing  to  the  same  result  can  be  adduced 
without  difficulty.  See  the  next  table  below,  also  by  E.  Meyer, 
who  has  done  an  immense  amount  of  work  in  the  investigation 
of  gas  engines.  Banki  took  advantage  of  the  principle  in  his 
gasoline  engine,  in  which,  by .  using  water  injection,  he  could 
employ  compression  ratios  similar  to  those  used  in  producer  gas 
work  and  realized  thermal  efficiencies  fully  equal  to  those  ob- 
tained with  the  leaner  power  gases. 

4.  The  Mixture.  —  The  inherent  advantage  of  the  use  of  lean 
mixtures  has  already  been  shown  in  Chapter  III.  Burstall  *  on 
the  basis  of  his  tests  for  the  British  Institution  of  Mechanical 
Engineers,  concludes  that  the  thermal  efficiency  depends  upon 
the  correct  choice  of  the  mixture,  and  that  the  ratio  of  air  to  gas 
should  increase  with  the  compression.  His  results,  however,  do 
not  definitely  warrant  the  latter  part  of  this  deduction,  although 
it  finds  some  support  in  the  above-mentioned  tests  by  Meyer,  f 
as  shown  by  the  following  table: 


Test  No. 

Ratio  of  Compression 

Ratio  Air  to  Gas 

Gas  Consumption  Cu. 
Ft.  per  I.  H.  P.-hour 

U;,. 

2.67 

6.41 

8.08 

27.1 
25.4 

!}- 

3.23 

6.38 

8.07 

22.6 
21.6 

8}-- 

3.87 

5.93 
8.29 

20.6 
18.5 

II-- 

4.32 

6.00 
8.35 

19.4 
17.9 

*  Proceedings,  1898,  p.  209.          f  E.  Meyer,  Z.  d.  V.  d.  I.,  1899,  p.  361. 


534  INTERNAL  COMBUSTION  ENGINES 

This  table  shows  that,  whatever  the  ratio  of  compression,  the 
gas  consumption  is  less  with  the  leaner  mixtures.  The  cause  for 
this,  besides  the  theoretical  reason,  may  possibly  be  found  in  the 
fact  that  with  leaner  mixtures  the  maximum  temperatures  in  the 
cycle  are  lower  than  with  rich  mixtures,  always  assuming,  of 
course,  that  the  mixture  contains  no  excess  gas. 

How  the  efficiency  of  an  engine  may  be  affected  by  careless 
setting  of  the  fuel  valve  is  well  shown  in  some  results  quoted 
by  Lucke.*  The  test  cited  is  on  a  10  I.  H.  P.  Otto  engine 
governed  by  hit  and  miss.  The  fuel  used  was  carbureted 
water  gas. 


Gas  Valve  Number 

Efficiency 

9 

16.0 

8 

16.5 

7 

18.0 

6 

19.0 

5 

10.0 

It  is  quite  evident  from  the  figures  that  the  last  setting  wasted 
a  lot  of  unburned  gas,  while  the  leaner  mixtures  were  inefficient, 
probably  due  to  sluggish  combustion.  The  same  thing  was 
noticed  in  a  series  of  tests  on  German  alcohol  engines,  in  which 
it  was  found  that  the  setting  of  the  fuel  needle  valve  had  a  pro- 
nounced effect  upon  the  economy. 

5.  Variation  of  Point  of  Ignition.  —  The  effect  on  the  appear- 
ance of  the  diagram  of  varying  the  point  of  ignition  has  already 
been  discussed.  To  get  some  idea  of  the  influence  of  varying 
time  of  ignition  on  engine  capacity  and  efficiency,  the  following- 
figures  are  given.  The  first  set  f  was  obtained  in  determining 
the  range  of  adjustment  of  the  igniter  gear  on  an  8"  x  12"  hori- 
zontal hit-and  miss-engine,  running  265  r.p.m.  on  natural  gas. 

*  Lucke,  Gas  Engine  Design. 

t  Obtained  through  the  courtesy  of  Mr.  A.  B.  Gould,  of  the  Wellman, 
Seaver,  Morgan  Co.,  Cleveland. 


PERFORMANCE  OF  GAS  ENGINES 


535 


Card  No. 

Crank  Angle  below  horizontal 
at  time  of  ignition 

Max.  brake  load  possible 
at  265  R.  P.  M. 

8 

35° 

47    Ibs.  net 

9 

33° 

47      ' 

10 

32° 

47i    '        ' 

11 

24° 

47    •  t 

12 

23° 

44J    '        ' 

13 

15° 

44      ' 

The  accompanying  indicator  cards  are  shown,  much  reduced, 
in  Fig.  17-1.     The  scale  of  spring  was  160  pounds. 


FIG.  17-1. 

The  second  set  of  figures  is  due  to  Mr.  J.  R.  Bibbins,  and  was 
published  by  him  in  the  Michigan  Technic  for  February,  1907. 
They  are  here  reproduced  by  permission  of  the  author,  obtained 
through  Mr.  R.  D.  Day  of  the  Westinghouse  Machine  Co.  The 
tests  were  made  on  a  9  x  11",  2-cylinder  Westinghouse  gas  engine. 
The  load  was  kept  constant  at  about  70  B.  H.  P.,  the  speed  was 
held  constant  at  about  300.  r.p.m.  The  gas  used  was  natural 


536 


INTERNAL  COMBUSTION  ENGINES 


gas  with  a  constant  lower  heating  value  of  934  B.  T.  U.  The 
point  of  ignition  was  changed  by  steps  from  dead  center  to  55  de- 
gree crank  angle  ahead  of  the  center,  that  is,  the  spark  was  ad- 
vanced to  that  extent.  The  following  table  shows  the  results: 


Point  of 
Ignition 
Degrees 

Load 
B.H.P. 

R.P.M. 

Gas  per 
B.  H.  P. 

per  hour 

B.T.  U.  per 
B.  H.  P.- 

hour 

Thermal 
Efficiency 
on  Brake 

Relative 
Efficiency 

PRESSURES  LBS. 
per  sq.  inch 

early 

cu.  ft. 

% 

Max. 

Release 

0 

70.0 

292 

14.38 

13410 

19.0 

.815 

151 

36 

8 

70.8 

295 

13.34 

12470 

20.4 

.875 

168 

36 

20 

71.0 

296 

12.36 

11530 

22.1 

.947 

177.5 

33.6 

25 

71.0 

296 

12.3 

11490 

22.2 

.951 

220.5 

31.2 

30 

71.3 

297 

11.71 

10940 

23.3 

1.000 

252 

31.2 

35 

71.3 

297 

12.03 

11230 

22.7 

.972 

252 

28.8 

45 

71.2 

296.5 

12.40 

11590 

21.9 

.942 

379 

28.8 

55 

70.0 

292 

15.74 

14700 

17.3 

.742 

437 

24.0 

The  results  of  the  test  are  shown  graphically  in  Fig.  17-2. 
The  best  lead  angle  for  the  sparking  gear  appears  to  be  between 
30  and  35  degrees,  in  which  this  test  agrees  closely  with  the  re- 


Cf/ect  of  I/triable  Ig 


Point  on  Gas  Ehsine 


Point  of  ft 'nit  ion-  Degrees  £ar 


W 


PERFORMANCE  OF  GAS  ENGINES 


537 


suits  obtained  by  Mr.  Gould  on  a  similar  engine.     Fig.  17-3  shows 
the  typical  indicator  card  accompanying  each  igniter  position. 

6.  Engine  Economy  depending  upon  Load.  —  As  is  the  case 
in  the  steam  engine,  the  efficiency  of  a  gas  engine  decreases  as 
the  load  decreases  below  the  normal.  The  amount  of  this  de- 
crease varies  in  different  engines,  depending  mainly  upon  the 


IGNITION     0 


I9NITIQN 


IGNITION    20   € 


IGNITION    25  *£ 


IGNITION    J0*£ 


IGNITION 


IGNITION    43    £ 


IGNITION    J5*£ 


FIG.  17-3. 


kind  of  fuel  used  and  the  system  of  governing  employed.  The 
following  set  of  curves,  Fig.  17-4,  makes  this  clear.  Regarding 
the  range  of  load  above  normal,  however,  it  is  found  that,  while 
a  steam  .engine  generally  shows  a  decrease  in  efficiency  for  over- 
loads, the  gas  engine  usually  shows  a  greater  efficiency  at  the 
maximum  load  than  at  the  normal;  in  other  words,  just  as  long 
as  a  gas  engine  keeps  up  the  normal  speed  under  an  increase  in 


538 


INTERNAL  COMBUSTION  ENGINES 


PERFORMANCE  OF  GAS  ENGINES 


539 


load  the  thermal  efficiency  will  rise  with  the  load.  A  few  typical 
efficiency  curves  are  shown  in  the  figure.  The  data  for  these  has 
been  collected  from  various  sources,  as  shown  in  the  accompany- 
ing table: 


Curve 
No. 

Type  of  Engine 

B.H.P. 

R.P.M. 

Fuel 

Governing 

Reference 

1 

Deutz,  Single 

50 

200 

111.  Gas 

Throttling 

E.  Meyer, 

Cylinder 

Gas. 

Z.  d.  V.  d.  I., 

1898. 

2 

Westinghouse 
3-cycl.  Vert. 

100 

270 

Natural 
Gas. 

Throttling 
Mix. 

Robertson, 
1899. 

3 

Deutz. 

450 

— 

Producer 

— 

Guarantee 

Gas. 

Fig.  for  en- 

tire plant. 

Josse,  1904. 

4 

Giildner,  Single- 

35 

220 

Producer 

Throttling 

Giildner,  1906, 

cylinder. 

Gas. 

for  plant  in- 

cluding 

generator. 

5 

Niirnberg. 

1200 

106 

Blast- 

Throttling 

Riedler, 

Furnace 

Gas. 

Gross-Gas- 

Gas. 

Maschinen, 

1905. 

6 

Swiderski,  Single- 

15 

235 

Alcohol. 

Hit&  Miss. 

E.  Meyer, 

cylinder. 

Z.d.V.d.L, 

1903. 

7 

Deutz,  Single- 

12 

285 

Alcohol. 

Throttling. 

« 

cylinder. 

8 

Diesel. 

70 

158 

Russian 

Cut-off. 

tt 

Kerosene. 

9 

Diesel. 

8 

275 

« 

a 

u 

10 

Hornsby-Akroyd 

25 

202 

Kerosene. 

Regulating 

Robinson, 

Oil. 

1898. 

11 

Bdnki. 

25 

210 

Gasoline 

Hit&  Miss. 

Jonas  and 

with  water 

Taborsky 

injection. 

Z.  d.  Oest. 

Arch.&  Ing 

V.,  1900. 

7.  The  Heat  Balance.  —  Accounting  for  the  heat  furnished 
to  a  heat  engine  is  called  constructing  the  Heat  Balance.  In  an 
internal  combustion  engine  the  heat  supplied  to  the  engine  is  that 
contained  in  the  fuel  furnished  to  the  engine  in  a  given  time. 
For  convenience  all  heat  calculations  are  referred  to  some 
standard  temperature,  usually  room  temperature.  It  is  usual 
to  account  for  the  heat  in  four  separate  items: 

1.  Heat  represented  in  indicated  work. 

2.  Heat  carried  off  in  the  jacket  water. 


540  INTERNAL  COMBUSTION  ENGINES 

3.  Heat  lost  in  exhaust. 

4.  Heat  loss  due  to  radiation,  conduction,  etc. 

Of  these  the  first  and  second  items  admit  of  accurate  determina- 
tion, the  fourth  is  nearly  always  found  by  difference  between  the 
sum  of  the  other  three  items  and  the  heat  supplied.  Item  three 
is  much  more  difficult  of  exact  determination.  Its  calculation 
involves  the  determination  of  the  weight  of  exhaust  gases  and  of 
the  specific  heat  of  these  gases  at  exhaust  temperature. 

The  only  accurate  way  to  find  the  weight  of  the  exhaust 
gases  is  by  metering  or  otherwise  determining  the  air  supply  to 
the  engine.  The  weight  of  the  exhaust  gases  is  in  all  cases  the 
weight  of  air  plus  the  weight  of  the  fuel. 

There  are  two  other  ways  sometimes  employed,  but  either  one 
can  only  give  approximate  results.  One  of  these  determines  the 
charge  weight  from  the  piston  displacement.  This  involves 

(a)  The  volumetric  efficiency  of  the  suction  stroke,  and 

(6)  Some  assumption  as  to  the  temperature  of  the  charge  at 
the  end  of  the  suction  stroke. 

It  is  possible  to  determine  the  volumetric  efficiency  with  fair 
accuracy  by  means  of  a  weak  spring  card,  but  the  second  point 
offers 'much  more  difficulty.  The  charge  at  the  end  of  the  suction 
stroke,  taking  the  case  of  a  gas  engine,  consists  of  a  certain  amount 
of  air,  of  fresh  gas,  and  of  burned  gases  from  the  clearance.  The 
entering  temperature  of  air  and  of  gas  can  be  accurately  deter- 
mined, but  the  temperature  of  the  mixture,  as  it  enters  the  cylin- 
der, changes,  due  to  contact  with  the  hot  walls  and  to  mixing 
with  the  clearance  gases.  Nothing  is  definitely  known  of  the 
weight  of  the  clearance  gases,  for  although  their  pressure  and 
volume  are  known,  nothing  is  known  of  the  temperature.  Hence 
neither  the  wall  effect  nor  that  due  to  the  clearance  gases  can  be 
definitely  gaged  and  all  temperature  computations  therefore 
become  approximate.  The  only  positive  way  of  determining 
the  temperature  at  the  end  of  the  suction  stroke  is  by  actual 
measurement.  This  has  been  successfully  done,  but  the  apparatus 
is  not  such  as  could  well  be  employed  in  ordinary  testing. 

It  must  be  evident,  therefore,  that  piston  displacement  meas- 
urement of  the  weight  of  the  exhaust  gases  can  be  approximate 
only.  To  cite  a  case  in  point,  the  test  of  Brooks  and  Stewart, 
mentioned  in  Chapter  V,  showed  an  actual  ratio  of  air  to  gas  on 


PERFORMANCE  OF  GAS  ENGINES  541 

test  of  6.63,  while  piston  displacement  computation  showed 
8.32. 

The  second  approximate  computation  for  the  weight  of  the 
exhaust  gases  is  based  upon  the  exhaust  gas  analysis.  The 
method  of  doing  this  has  been  explained  in  detail  in  Chapter  VI. 
The  trouble  with  this  scheme  lies  in  the  difficulty  of  obtaining 
representative  gas  samples.  But  granting  even  that  these  are 
obtained,  it  is  often  found  that  computations  based  upon  the 
analyses  show  an  excess  coefficient  smaller  than  that  really  used. 
That  is,  the  weight  of  exhaust  gases  so  determined  is  less  than 
the  actual  amount.  Thus,  Schottler,  in  computation  on  some 
of  Slaby's  tests,  shows  in  one  case  that,  based  upon  analysis,  the 
excess  coefficient  was  5.52,  while  in  reality  it  was  6.2.  Schottler 
attributes  this  discrepancy  to  a  change  in  the  analysis  due  to  a 
burning  up  of  the  lubricating  oil,  which  is  apt  to  increase  the 
CO2  content  of  the  exhaust  gas  at  the  expense  of  the  percentage 
of  O.  It  has  been  shown  that  a  variation  in  the  supply  of  lubri- 
cating oil  may  change  the  fuel  consumption  under  circumstances 
quite  materially,  and  Schottler's  surmise  is  therefore  probably 
correct.  At  the  same  time,  however,  any  such  effect  must  be 
more  marked  in  the  smaller  machines,  and  the  writer  believes 
that,  given  representative  samples  of  exhaust  gas  from  any- 
thing but  the  small  machines,  in  conjunction  with  accurate  fuel 
analysis,  a  very  close  approximation  to  the  actual  weight  of 
the  exhaust  gases  can  be  obtained.  At  any  rate  the  method 
should  be  more  accurate  than  that  based  on  piston  displace- 
ment. 

Finally,  it  should  not  be  forgotten  that  even  an  accurate 
determination  of  the  air  supply  still  leaves  open  the  question  of 
the  specific  heat  of  the  exhaust  gases. 

The  heat  balance  of  the  four  items  above  outlined  is  sometimes 
shortened  to  three  by  combining  items  3  and  4  and  determining 
their  sum  by  difference.  On  the  other  hand,  a  balance  of  many 
more  items  can  be  drawn  up.  Thus  each  event  of  the  cycle  may 
be  examined  by  itself  and  the  heat  and  energy  interchanges  be 
determined.  A  very  detailed  balance  of  this  kind  is  given  in 
Schottler's  "Die"  Gasmaschine,"  p.  321.  How  far  this  question 
needs  to  be  entered  into  depends  altogether  upon  the  importance 
of  the  test,  but  an  effort  should  be  made  in  every  case  to  so  arrange 


542  INTERNAL  COMBUSTION  ENGINES 

the  apparatus  that  at  least  a  heat  balance  of  the  kind  first  dis- 
cussed can  be  drawn  up  from  the  results  of  the  test. 

8.  Results  of  Tests  of  Engines  and  Gas  Producers.  —  By  this 
term  is  here  meant  the  results  shown  by  engines  or  producers 
when  operated  under  normal  conditions  and  at  or  near  normal 
load.  The  number  of  tests  from  which  this  data  can  be  obtained 
is  at  the  present  writing  quite  large,  and  some  notable  collections 
of  test  data  have  been  made.  The  mcst  extensive  is  perhaps  that 
contained  in  Appendix  A  of  Brian  Donkin's  "Gas,  Oil  and  Air 
Engines."  This  collection  consists  of  eleven  tables,  arranged 
according  to  fuel  used,  containing  in  all  some  280  tests.  Another 
large  collection  is  that  found  appended  to  Witz's  "  Moteurs  a  Gas 
et  a  Pet  role. "  Such  collections  are  valuable  as  showing  what 
has  been  done,  and  serve  as  a  guide  as  to  what  may  be  expected 
from  an  engine  under  design  or  construction.  The  greatest  care, 
however,  should  be  exercised  to  see  that  only  reliable  data  is 
incorporated. 

ENGINE  TESTS. — Table  I  (pp.  544  and  545)  contains  a 
series  of  engine  test  data  taken  from  various  sources.  The 
tests  are  arranged  according  to  the  kind  of  fuel  used,  this 
being  the  most  logical  way.  In  some  cases  not  all  the  data 
is  given  in  the  original  report.  Wherever  possible  computations 
have  been  made  to  make  the  items  complete.  In  many  cases, 
however,  not  enough  information  is  given  to  permit  of  this,  and 
the  record  necessarily  remains  incomplete. 

TESTS  OF  PRODUCERS  AND  PRODUCER  PLANTS.  —  Table  II, 
p.  546,  gives  some  of  the  results  obtained  on  tests  of  producers. 
In  some  cases  the  tests  refer  to  producers  only,  giving  no  data 
regarding  the  engine  used;  in  others  the  data  is  fairly  complete 
for  the  entire  plant. 


PERFORMANCE  OF  GAS  ENGINES 


543 


In  conclusion,  Fig.  17-5  shows  a  set  of  curves  drawn  by  C.  H. 
Day  in  1905  during  an  investigation  on  the  economy  of  producer 
gas.  The  curves  show  the  relation  between  cubic  feet  of  gas  used 
arid  brake  horse-power  for  various  kinds  of  gas.  While  it  must 
be  understood  that  they  are  approximate  only,  they  represent 
a  fair  general  average  of  what  is  accomplished  to-day.  Many 
plants  show  much  better  fuel  consumption,  but  others  show 


FIG.  17-5. 

correspondingly  worse.  The  curves  also  show  in  a  measure  the 
sizes  up  to  which  the  various  engines  are  built.  Thus  an  illu- 
minating gas  engine  of  150  horse-power  is  a  large  engine  of  its 
type.  Producer  plants  in  1905  apparently  were  not  built  much 
larger  than  500  horse-power,  while  natural  gas  and  blast  furnace 
gas  engines  were  built  exceeding  1000  horse-power,  and  for  the 
latter  gas  2000  and  3000  horse-power  is  not  now  out  of  ordinary. 


TABLE    I. 


DIMENSIONS  ANU  OTHER  DATA 

Name 

Rated 

Kind  of  Fuel 

of 

B.H.P 

R.p.m. 

Engine 

Dia.of 
Cyl. 
Inch. 

Stroke 
Inch. 

No.  of  Cyls. 

2  or  4-cycle 

Single  or 
Oouble  Act. 

Illuminating  Gas 

Koerting 

— 

— 

— 

4 

s 

— 

161 

Illuminating  Gas 

Deutz 

4.96 

5.92 

1 

4 

S 

2 

260 

Illuminating  Gas 

Giildner 

— 

— 

1 

4 

S 

15 

— 

Illuminating  Gas 

Giildner 

10 

15.7 

1 

4 

S 

20 

210.7 

Illuminating  Gas 

Banki 

— 

— 

1 

4 

S 

16 

255 

Illuminating  Gas 
Illuminating  Gas 
Illuminating  Gas 

Tangye 
Crossley 
Westinghouse 

10 

7 

19 
15 

1 
3 

4 
4 
4 

S 
S 

S 



193.6 
200 
235 

Natural  Gas 

Westinghouse 

25 

30 

3 

4 

S 

550 

150 

Natural  Gas 

Snow 

25 

48 

4 

4 

— 

— 

— 

Natural  Gas 

Otto 

11.25 

18 

1 

4 

S 

36 

220.4 

Natural  Gas 

Walrath 

13 

14 

3 

4 

s 

75 

253.3 

Producer  Gas 

R.  D.  Wood 

25 

30 

2  (Tandem) 

4 

s 

300 

149 

Producer  Gas 

Westinghouse 

— 

— 

3 

4 

s 

— 

235 

Producer  Gas 

Crossley 

26 

36 

— 

4 

s 

— 

152.4 

Producer  Gas 

Koerting 

21.6 

37.7 

1 

2 

D 

— 

101 

Producer  Gas 

Deutz 

_ 





4 

• 



,  161.6 

Coke  Oven  Gas 

Oechelhauser 

65 

37.5 

1 

2 

2  pistons  in 

500 

110.6 

(Borsig) 

1  cylinder 

Mond  Gas 
Mond  Gas 
Blast  Furnace  Gas 

Crossley 
Crossley 
Nurnberg 

16.9 
26 
33.5 

24 
36 
43.4 

2  (Opposed) 
2  (Opposed) 
2  (Tandem) 

4 
4 
4 

S 
S 
D 

400 

162 
148.5 
105.6 

Blast  Furnace  Gas 

Berlin-Anhalt 

16.95 

27.5 

1 

4 

S 

60 

160.6 

Blast  Furnace  Gas 

Cockerill 

51.2 

55.2 

1 

4 

D 

— 

94.57 

Gasoline 

Fairbanks 

6.5 

9 

1 

4 

S 

7 

300 

Gasoline 

Springfield 

6.5 

12 

1 

4 

S 

6 

"230.4 

Gasoline 

Lozier 

5 

6 

1 

2 

S 

5 

513 

Gasoline 

Westinghouse 

5.75 

8 

2 

4 

s 

10 

289.7 

Gasoline 

Banki 

.  .— 

— 

1 

4 

s 

— 

209.1 

Gasoline 

Daimler 

3.56 

5.11 

4 

4 

s 

16-20 

400 

Gasoline 

Daimler 

3.56 

5.11 

4 

4 

s 

16-20 

600 

Gasoline 

Daimler 

3.56 

5.11 

4 

4 

s 

16-20 

1000 

Kerosene 

Diesel 

10.23 

16.16 

1 

4 

s 

186.6 

Kerosene,  Russian 

Diesel 

15.75 

23.65 

1 

4 

s 

70 

158.8 

Kerosene,  Russian 

Diesel 

6.65 

10.60 

1 

4 

s 

8 

270.3 

Kerosene 

Priestman 

10.9 

14.1 

1 

4 

s 

172 

Kerosene 

Grob  &  Co. 

9.07 

9.07 

1     , 

4 

s 

8 

266 

Kerosene 

Swiderski 

10 

10 

1 

4 

s 



249 

Kerosene 

Koerting 

6.9 

10.82 

4 

s 



222 

Kerosene 

Blackstone 

7 

12 

1 

4 

s 



240 

Kerosene 

Stevenson 

9.5 

18 

1 

4 

s 



200 

Kerosene 

Hornsby 

8.2 

14 

1 

4 

s 

— 

213.8 

Kerosene 

Hornsby 

14.5 

17 

1 

4 

s 

25 

202.6 

Crude  Oil 

Diesel 

— 

— 

— 

4 

s 

225 

169.1 

Alcohol,  86.1  vol.  % 

Deutz 

8.35 

11.8 

1 

4 

s 

12 

276.9 

Alcohol,  86.1  vol.% 

Marienfelde 

9.95 

15.75 

1 

4 

s 

14 

197.6 

Alcohol,  86.1  vol.% 
Alcohol,  87  vol.  % 

Koerting 
Banki 

6.16 

9.95 

4 
4 

s 
s 

6 
20 

307.3 
225 

544 


ENGINE  TESTS 


LOWER 

HEATING 

. 

H.P.  ON  TEST 

VALUE  OF 

HEAT  DISTRIBUTION.  % 

tesS 

IU^L   B.T.U. 

Mech. 

—  fit 

PER 

Eff. 

gsd 

References  and  Remarks 

-*cu 

% 

j8™ 

I.H.P. 

B.H.P. 

Lb. 

Cu.  ft. 

Is 

Jacket 

Exhaust  Rest 

£s 

— 

108.1 

— 

500 

— 

— 

—          — 

— 

28.22 

De    La    Vergne    Machine 

Co.,  Cat. 

2.30 

1.72 

— 

572 

21.5 

50.4 

25.0         4.1 

75 

16.1 

Wimplinger,        Zeitschrift 
d.  V.  d.  I.   Sept.  8,  1906. 



,  



580 

40.5 

.  







Dubbel      Z    d     V    d    I 

Nov.  3,  1906. 

35.9 

— 

— 

— 

42.7 

33.2 

24.1 

— 

— 

Test     by     Schroter,   Z.  d. 
V.  d.  I.,  June,  1904. 

— 

17.03 

— 



— 

27.97 

—         — 

— 

31.0 

Schimanek,  Z.  d.  V.  d.  I., 

Jan.  17,  1903. 

28.6 

25.4 



609 







85 

24.5 

Witz,   1902. 

14 

12 

680 







86 

22 

Clerk,   1894. 

196.5 

147.5 

— 

597.4 

35 

— 

—          — 

76 

26.7 

Ballinger    &  Hunt,  Sibley 

College  Thesis,    1904. 

618 

550 



1000 

27.1 





89 

24.1 

J.    R.    Bibbins,    A.I.E.E., 

Dec.  1903. 

736.7 

594.5 

— 

1175(?) 

29.4 

— 

—      '  •  — 

80.7 

23.7 

Hastings    &   Parker,    Sib. 

Coll.  Thesis,  1901. 

36.3 

28.8 

.  —  . 

1086 

20.2 

— 

—          — 

79.5 

16.1 

Hunting,  Sib.  Coll.  Thesis, 

1902. 

86.7 

78.7 

— 

1041 

27.1 

49.5 

23.4 

78.7 

21.3 

Geer     &    Vanelain,     Sib. 

Coll.  Thesis,  1902. 

242 

169 

— 

145 

24.4 

25.0 

50.6 

70 

17.1 

Goldsmith       &    Hartwig, 

Sib.  Coll.  Thesis,  1905. 

173.6 

124.8 

— 

123.8 

33 

— 

—          — 

71.8 

23.7 

Ballinger     &    Hunt,    Sib. 

Coll.  Thesis,  1904. 

377.9 

313 

— 

90.13 

— 

— 

—          — 

83 

21.78 

Humphrey,     Inst.     Mech. 

Engs.,  1900. 

481 

341 

— 

129.5 

— 

— 

—          — 

71 

24.1 

E.    Meyer,  Jour,    fur  Gas 

Belenchtung,    1900. 

81 

70.4 



113 







87 

29 

E.  Meyer,   1903. 

765  (net) 

628 

— 

376 

33.4 

— 

—          — 

82.1 

27.5 

E.    Meyer,    Z.  d.  V.  d.  I., 

(Blowing 

Feb.  1905.  Test  No.  Vllb. 

Cyl). 

141.6 

— 

135 

29.1 

— 

—          — 





|  Humphrey's  Test,  Schott- 

440 

364 

_ 

138 

28.6 

— 

— 

83 

23.7 

ler,  Z.  Jan.  1902. 

1427 

1186 

— 

88 

33.9 

— 

—          — 

83.1 

28.2 

Riedler,  Gross-gasmaschi- 

nen,  p.  158. 

79.5 

54.5 

— 

102 

— 

— 

.  —          — 



26.2 

E.  Meyer.  Z.  1899,  p.  448. 

786.16 

575 



99.5 









20.4 

Hubert,  March,  1900. 

11.28 

7.23 

18200 

20.5 

— 

—          — 

64 

13.15 

Elwood,     Ford,     Garrow, 

Sib.  Coll.  Thesis,   1907. 

9.63 

6.16 

20078 

— 

15.8 

— 

—          — 

64 

10.2 

Keeley  &  Spier,  Sib.  Coll. 

Thesis,  1900. 

6.28 

4.92 

18520 

— 

19.8 

— 

—          — 

78.9 

15.7 

Bayne     &    Speiden,    Sib. 

Coll.  Thesis,  1902. 

9.19 

5.58 

— 

— 

28.5 

— 

—          — 

60.7 

17.3 

Glasgow    &   Powley,   Sib. 

Coll.  Thesis,    1902. 

— 

26.4 

— 

— 

— 

— 

—          — 

— 

28 

Jonas     &    Taborsky,     Z. 

Oest.  Arch.&Ing.  Verein, 

p.  512,  1900. 

= 

- 

17500 
17500 
17500 

= 

19.3 
22.0 
24.2 

5 

=     = 

86.1 
85.4 
79.8 

16.6 
18.8 
19.3 

I  Prof.       B.      Hopkinson, 
J      Cambridge,  1906. 

30.46 

20.81 

18604 



37.7 

. 

—          — 

68.3 

25.8 

Cat.  American  .Diesel  En- 

gine Co. 

88 

69.6 

18610 

— 

40.3 

— 

—          — 

79.1 

31.9 

I  E.  Meyer,  Z.  d.  V.  d.  I., 

11.19 

8.6 

18610 



35.8 





77.0 

27.6 

>      Mav,  1903. 

10.69 

10.18 

19800 

— 

— 

—          — 

95.2(?) 

13.4 

Hartman,   Z.  d.  V.  d.  I., 

1895.  p.  586. 

11.68 

9.22 

19800 

— 

— 

— 

—          — 

79 

13.6 

Hartman,   Z.  d.  V.  d.  I., 

1895,  p.  616. 

— 

10 
4.15 

19600 
19600 

— 

— 

— 

—          — 

— 

15.8 
9.9 

|  Schottler,     die      Gasma- 
»      schine,   p.   207. 

— 

3.05 

18000 

— 

— 

— 

—          — 

— 

19.7 

*  Engineering,     Vol.      88, 

— 

12.44 

18000 

— 

— 

— 

—          — 

— 

9.2 

»      1899. 

6.07 

4.95 

18600 

— 

16 

29 

55 

81.5 

13 

Robinson,    1893,   Gas   & 

Pet.  Engines,  p.  702. 

31 

26.74 

18870 



21 

50 

29 

86.0 

18 

Robinson,  1898,  Gas  & 

249.7 

19460 

28.1 

Pet.  Engines,  p.  710. 
Kimberley  &  Clark  Paper 

Co.,    Kimberley,    Wis., 

Power,  Oct.  1906. 

— 

16.8 
19.77 
7.39 

9900 
9900 
9900 

= 

= 

= 

=     = 

= 

31.6 
32.7 
21.8 

1  E.  Meyer,  Z.  d.  V.  d.  I., 
April,  1903. 

— 

32-13 

9700 

— 

— 

32.1 

—          — 

— 

30.18 

Schimanek,  Z.  d.  V.  d.  I., 

Jan.  17,  1903. 

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1   i 


CHAPTER  XVIII 

COST   OF   INSTALLATION    AND    OF    OPERATION 

i.  Cost  of  Producers  and  Engines.  —  With  the  approach  to 
standardization  of  the  design  of  the  internal  combustion  engine 
there  has  also  come  a  tendency  toward  standard  prices.  The 
figures  available,  however,  for  anything  but  small  engines  are  not 
plentiful.  This  is  no  doubt  due  to  the  fact  that  large  installations 
are  as  yet  not  numerous  and  information  is  correspondingly 
scarce.  The  writer  has  been  able  to  glean  the  following  data 
from  current  literature: 

PRODUCERS.  —  The  Gas  Engine,  June,  1906,  gives  the  follow- 
ing figures  for  producers: 

Pressure  Producers,  erected  complete  but  not  including  freight, 
$25  per  horse-power  for  hard  coal,  and  $27  per  horse-power  for 
soft  coal  producers.  These  figures  are  for  sizes  in  the  neighbor- 
hood of  300  horse-power.  The  cost  is  distributed  approximately 

as  follows: 

25  per  cent  in  the  producer. 

15  per  cent  in  the  scrubber. 
30  per  cent  in  the  gas  holder. 
30  per  cent  in  piping  and  fittings. 

The  increased  cost  of  the  bituminous  coal  plant  is  mainly  due  to 
greater  cost  of  washing  apparatus. 

Suction  Gas  Plants  will,  on  a  rough  estimate,  cost  only  about 
one-half  the  above.  The  reasons  for  this  are  greater  capacity  of 
producer  and  the  elimination  of  the  gas  holder.  One  maker  gives 
the  following  approximate  figures  for  the  price  of  suction  gas 
plants  from  25  to  250  horse-power. 

400 

Price  per  horse-power  =  $  11  +  ==— - 

xl.r^. 

Thus  a  25  horse-power  plant  would  cost  $37.00  per  horse-power, 
and  one  of  250  horse-power  $12.60  per  horse-power.  In  the 
writer's  experience  practice  agrees  fairly  well  with  these  figures. 

547 


548  INTERNAL  COMBUSTION  ENGINES 

ENGINES.  —  The  cost  of  stationary  gas  engines  at  present 
seems  to  range  from  about  $70  per  horse-power  for  very  small 
engines  to  in  the  neighborhood  of  $25  per  horse-power  for 
large  ones.  Recent  quotations  on  producer-gas  engines  for  in- 
stance showed  the  cost  to  be  about  $55  per  horse-power  for  a 
10  horse-power  engine,  and  $36  per  horse-power  for  a  50  horse- 
power machine.  The  latter  is,  however,  a  comparatively  low 
price  for  an  engine  of  this  size.  The  price  of  launch  engines  is 
frequently  lower  than  this,  from  $50  per  horse-power  for  the  small 
engine  to  about  $20  per  horse-power  for  an  engine  of  25  to  30 
horse-power.  The  cost  of  Diesel  engines  runs  somewhat  higher, 
varying  probably  between  $50  and  $90  per  horse-power,  depend- 
ing upon  size.  None  of  these  figures  include  cost  of  erection. 

Suction  Gas  Plants.  —  Recent  quotations  for  plants  of  this 
type  have  been  for  a  10  horse-power  plant,  which  is  below  the 
ordinary  commercial  size,  $90  per  horse-power  for  a  50  horse- 
power plant  $51  per  horse-power  and  again  $61  per  horse-power, 
and  for  a  75  horse-power  plant  $53  per  horse-power. 

2.  Cost  of  Erection. — The  cost  t  of  erection  varies  largely 
with  the  size  of  the  foundations.     Regarding  the  latter  there 
seems  to  be  no  definite  proportionality  between  it  and  the  size 
of  the  engine.     In  general,  of  course,   vertical  engines  do  not 
require  as  large  or  as  heavy  a  foundation  as  horizontal  engines, 
but  the  condition  of  the  ground  has  a  great  deal  to  do  with  the 
final  cost.     Giildner  *  estimates  that  from  15  to  20  cubic  feet  of 
foundation  per  brake  horse-power  of  engine  should  be  sufficient 
in  the  ordinary  case  if  the  ground  is  safe.     For  large  machines, 
however,  this  may  even  be  as  low  as  8  cu.  ft.  per  B.  H.  P.     The 
total  cost  of  erection  and  starting  should  not  exceed  about  3  per 
cent  of  the  purchase  price  in  the  case  of  gasoline  and  gas  engines, 
and  should  not  be  over  5  per  cent  in  the  case  of  producer  gas 
plants.     These  figures  agree  fairly  well  with  the  estimates  made 
by  H.  A.  Clark  in  1903.f 

3.  Piping  and  Auxiliaries.  — This  item  is  apt  to  vary  within 
wide  limits,  especially  in  producer  gas  plants,  where  much  de- 
pends upon  the  location  of  the  producer  plant  with  reference  to 

*  Verbrennungsmotoren,  p.  433. 

fH.  Ade  Clark,  The  Diesel  Engine,  Proceedings  of  Mechanical  Engineers, 
1903. 


COST  OF  INSTALLATION  AND  OF  OPERATION      549 

the  engine.  In  a  normal  case,  5  per  cent  of  the  cost  price  of  the 
engine  or  plant  should  cover  the  cost.  This,  however,  does  not 
include  the  cost  of  an  air  compressor  system  if  this  is  required  to 
start  the  plant. 

4.  Floor  Space  and  Buildings.  —  The  cost  of  buildings  is 
intimately  connected  with  the  floor  space  required  by  the  plant, 
but  outside  of  this  nothing  very  definite  can  be  said  of  the  cost  of 
the  building,  since  everything  depends  upon  the  construction 
used.  The  cost  based  on  the  square  foot  of  floor  space  may  vary 
from  about  $1.50  for  a  plain  brick  building  with  steel  roof,  to 
$2.75  for  a  modern  steel  concrete  structure.  Among  the  figures 
available  are  the  following.  A.  H.  Clark,  in  the  article  already 
mentioned,  estimates  the  cost  of  building  as  follows: 


Size  of  Engine 

Cost  of  Engine, 

Cost  of 

Ratio  C°Stof  Bldg- 

B.  H.  P. 

Accessories 

Building 

U°  Cost  of  Plant 

Producer  Gas  *  .  . 

35 

$2,360 

$   640 

.27 

Diesel 

35 

2  860 

440 

16 

Producer  Gas  .  .  . 

80 

4,400 

930 

.21 

Diesel  

80 

4,400 

685 

.16 

Producer  Gas  .  .  . 

160 

7,450 

1,150 

.16 

Dies-1  

160 

8,300 

880 

.11 

Giildner,  in  making  a  similar  estimate,  combines  the  cost  of 
building  and  of  necessary  foundations  for  the  engine  and  pro- 
ducer. Expressing  this  combined  cost  in  per  cent  of  the  cost  of 
plant  and  accessories,  the  following  table  shows  the  results: 


Horse-power  of  Plant 

Type  of  Plant 

5 

10 

15 

20 

25 

30 

40 

50 

100 

125 

150 

175 

200 

Illuminating  Gas  Engine 

27 

22 

20 

19 

18 

17 

16 

15 

13 

13 

13 

13 

13 

Suction  Gas  Plant  Complete 

30 

26 

24 

22.5 

21 

19.5 

19 

18 

15.5 

15 

15 

15 

14.5 

Turning  next  to  the  floor  space  required,  there  is  considerable 
data   available   in   the   literature   published.     Collaborating   the 


*  Pressure  producer. 


550 


INTERNAL  COMBUSTION  ENGINES 


figures  given  by  manufacturers  for  the  floor  space  required  for 
horizontal  single-cylinder  gas,  gasoline  and  oil  engines,  and  for 
suction  gas  producers,  we  obtain  Curves  I  and  III  of  Fig.  18-1. 


£10 

a 


I.    ACTUAL  SPACE,   SUCTION  PRODUCERS 
II.   SIZE  OF  PRODUpER  ROOM 

III.  ACTUAL  SPACE,  HORIZONTAL  ENGINES 

IV.  SIZE  OF  ENGINE  ROOM 


100       120      140      160 

BRAKE  HORSE  POWER 
FIG.  18-1. 


It  should  be  remembered  in  connection  with  these  curves,  how- 
ever, that  they  represent  average  figures  only  and  they  can  there- 
fore give  only  approximate  results.  For  example,  a  20  B.  H.  P. 


COST  OF  INSTALLATION  AND  OF  OPERATION      551 

suction  gas  producer  will,  according  to  Curve  I,  occupy  approxi- 
mately 20  X  2  =  40  sq.  ft.  of  floor  space,  say  a  space  9  X  4£  ft.; 
^similarly,  a  200  B.  H.  P.  installation  would  require  200  X  .8  =  160 
sq.  ft. 

In  like  manner  Curve  III  gives  the  approximate  floor  space 
for  horizontal  engines.  Thus  a  5  B.  H.  P.  gasoline  engine  of 
standard  make  would  probably  require  5  X  4  =  20  sq.  ft.,  say  a 
space  3  ft.  by  6  ft.;  while  a  150  B.  H.  P.  producer  or  illuminating 
gas  engine  calls  for  150  X  1.5  =  225  sq.  ft.  The  curve  does  not 
include  multi-cylinder  engines  because  the  available  figures  for 
this  type  of  engine  are  very  erratic.  For  the  same  reason  no 
curve  could  be  drawn  for  vertical  engines. 

While  Curves  I  and  III  represent  the  space  actually  occupied 
by  the  plant,  they  give  no  idea  of  the  size  of  the  producer  or 
engine  room  required.  In  the  producer  room  space  must  be  left 
for  the  proper  cleaning  of  the  producer,  etc.,  and  in  the  engine 
room  space  for  dismantling,  etc.  On  this  point  the  only  infor- 
mation that  seems  available  is  that  given  by  Giildner  in  his  esti- 
mates, the  results  of  which  are  plotted  in  Curves  II  and  IV  of 
Fig.  18-1.  The  former  shows  the  approximate  room  allowance 
for  suction  gas  apparatus,  the  latter  for  horizontal  single-cylinder 
engines,  based  on  one  brake  horse-power  in  each  case. 

The  data  available  for  pressure  producers  is  not  so  extensive 
as  that  for  suction  producers.  In  the  former  plants  much  depends 
upon  the  size  of  the  gas  holder.  Outside  of  this  the  space  re- 
quired for  suction  and  pressure  producers  should  not  vary  greatly. 
The  figures  at  hand  seem  to  indicate  that  pressure  producer 
plants,  including  the  gas  holder,  of  from  30  to  40  horse-power 
occupy  75  per  cent  more  space  than  suction  plants  of  like  capacity. 
As  the  power  increases  the  difference  grows  less,  a  plant  of  100 
horse-power  requiring  apparently  only  about  50  per  cent  more 
space,  and  one  of  175  horse-power  only  20  per  cent  more. 

The  minimum  head  room,  i.e.,  the  height  of  the  room  required 
for  either  type  of  plant,  seems  to  vary  from  12  ft.  in  the  small  20 
horse-power  plant  to  18  ft.  in  the  large  250  horse-power  producer. 

In  Power  for  April,  1907,  L.  L.  Brewer  published  the  following 
table  of  "Practical  Data  for  Modern  Gas  Engines."  The  table 
gives  in  column  13  figures  for  the  floor  space  required  by  engines 
larger  than  those  so  far  discussed.  The  letters  in  column  7  have 


552 


INTERNAL  COMBVSTION  ENGINES 


the  following  meaning:  s.c.,  single  cylinder;  tw.,  twin;  td.,  tandem; 
d.  td.,  double  tandem. 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

. 

c 

« 

* 

«1? 

w  c  8 

>£ 

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1 

^ 

^ 

3 

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'Srf 

"I   oc£ 

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bC"£ 

bfl_ 

w 

^ 

£ 

E 

U 

O 

Q 

b 

w£ 

fe|W 

E! 

w|^ 

W|OM 

^ 

E 

§ 

Builder 

— 
c 

a 

s. 

V 

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*! 

^Effl 

"^ 

Effi 

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3 
"?£ 

1 

bo'tj 

^1 

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ifils 

l.p« 

111 

111 

"a 

I 

^ 

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C/3 

U 

£ 

» 

^  ' 

£ 

^ 

f 

100 
200 
250 
300 
300 
300 
600 
600 
600 
600 
600 
600 
750 
1200 
1200 
1200 
1200 

150 
105 
150 
120 
120 
140 
80 
130 
110 
130 
130 
110 
90 
80 
130 
120 
110 

Cockerill.    .    .. 
Cockerill.    .    .. 
Cockerill.    .    .. 
Deutz  
Deutz  
Deutz  
Cockerill  
Cockerill  
Oechelhauser  .  . 
Deutz  
Deutz  
Koerting  
Niirnberg  
Cockerill  
Deutz  .  .  
Nurnberg  
Oechelhauser  .  . 

1 

1 

1 
2 
4 
1 
2 
1 
2 
4 
1 
1 
2 
4 
4 

4 
4 
4 
4 
4 
4 
4 
4 
2 
4 
4 

4 

4 
4 
4 

S. 
S. 
S. 

s. 
s. 
s. 
s. 

s. 
s. 
s. 

d. 

s. 
s. 
s. 
s. 
s. 

sc. 
sc. 
td. 
sc. 
tw. 
d.  tw. 
sc. 
td. 
sc. 
tw. 
d.  tw. 
sc. 
sc. 
td. 
d.  tw. 
d.  tw. 
tw. 

45,000 
83,000 
65,000 
83,500 
101,000 
110,000 
207,000 
185,000 
143,000 
158,000 
189,000 
136,500 
297,000 
365,000 
354,000 
280,000 
260,000 

9,000 
25,000 
10,000 
35,000 
14,000 
3,500 
100,000 
46,000 
48,000 
28,000 
7,000 
18,000 
115,000 
'  95,000 
14,000 
16,000 
16,000 

21,100 
58,500 
23,400 
81,800 
32,800 
8,200 
234,000 
107,500 
112,000 
65,500 
16,400 
42,200 
26,900 
222,000 
32,800 
37,400 
37,400 

540 
540 
300 
295 
383 
484 
512 
386 
318 
310 
327 
258 
560 
383 
307 
246 
230 

661 
706 
353 
551 

447 
394 
734 
487 
425 
371 
342 
297 
538 
488 
322 
264 
248 

2.05 
1.81 
1.24 
2.07 
1.52 
1.32 
0.99 
1.13 
1.23 
1.67 
1.08 
1.11 
1.03 
0.68 
1.01 
0.94 
0.9 

1200 
1400 

110 
110 

Koerting  
Cockerill  

2 

2 

2 
4 

d. 

d. 

tw. 
td. 

250,000 
374,000 

4,500 
8,600 

10,500 
20,000 

212 
170 

218 
164 

0.9 
0.42 

It  will  be  noted  from  column  6  that  there  is  only  one  double- 
acting  four-cycle  engine  in  the  list.  The  large  engines  cited  are 
all  single-acting  twin  or  tandem,  or  double  engines.  It  would 
naturally  be  assumed  that  the  later  types  of  large  four-cycle 
engines,  which  are  nearly  always  double-acting  tandem,  or 
double-acting  twin  tandem  machines,  should  show  a  decrease 
in  the  floor  space  required  as  compared  with  the  figures  in 
column  13.  An  indication  of  the  saving  in  both  weight  and 
floor  space  that  may  be  effected  by  adopting  the  double-acting 
principle  is  given  by  the  figures  for  the  1400  B.  H.  P.  double- 
acting  tandem  Cockerill  engine  in  the  last  line  of  the  table.  The 
saving  there  shown  is  remarkable  and  the  writer  has  not  been 
able  to  check  it  in  the  case  of  other  engines  the  design  of  which 
has  been  changed  from  the  twin  or  double-twin  single-acting  to 
the  double-acting  tandem.  The  reason  for  this  probably  is  that 
opposed  single-acting  engines  usually  work  without  a  cross-head, 


COST  OF  INSTALLATION  AND  OF  OPERATION      553 

while  double-acting  cylinders  demand  the  use  of  the  same.  Hence 
the  total  length  of  engine  is  not  changed  materially. 

5.  Cost  of  Operation.  —  The  total  cost  of  operation  consists 
of  the  following  items: 

(a)  Interest  on  capital. 

(6)  Depreciation  of  Plant  and  Buildings. 

(c)  Insurance. 

(d)  Fuel  Cost. 

(e)  Cost  of  Cooling  Water. 

(/)  Lubricating  Oil  and  Waste. 

(g)  Attendance. 

(h)  Maintenance  and  Repairs. 

Of  these,  the  first  three  items  are  usually  called  the  fixed 
charges,  and  the  last  five  the  operating  or  works  cost.  The  sum 
of  fixed  charges  and  works  cost  is  the  total  operating  cost. 

(a)  INTEREST  ON  CAPITAL.  The  usual  allowance  in  this  country 
for  interest  on  capital  is  6  per  cent. 

(6)  DEPRECIATION  OF  PLANT  AND  BUILDINGS.  There  is  little 
doubt  that  as  far  as  gas  producers  are  concerned,  the  wear  and 
tear  on  this  part  of  the  plant  is  much  less  than  it  is  on  a  boiler 
plant  of  the  same  capacity.  On  the  other  hand,  the  stresses  in  a 
gas  engine  are  generally  higher  throughout  than  those  in  a  steam 
engine  of  the  same  power,  and  this  naturally  leads  to  a  shorter 
life  and  consequently  somewhat  higher  allowance  for  deprecia- 
tion. Taking  it  altogether,  an  allowance  of  from  7  to  10  per  cent 
of  the  capital  outlay  for  the  power  plant  should  cover  deprecia- 
tion, the  lower  figure  for  a  producer  plant,  the  higher  where 
engines  alone  are  concerned. 

Depreciation  on  the  building  should  not  exceed  2  to  3  per  cent 
of  the  building  cost.  In  case  the  building  is  rented,  the  rent 
instead  of  depreciation  should  be  charged  against  the  plant. 

(c)  INSURANCE.     This  item  is  usually  very  small  as  compared 
with  the  rest  and  is  therefore  in  most  cases  neglected. 

(d)  FUEL  COSTS.     This  item  is  very  often  used  as  the  sole 
criterion  of  the  economic  status  of  a  plant,  but  in  many  cases  this 
is  not  true.     Where  the  cost  of  fuel  is  very  high,  as  for  instance 
where  illuminating  gas  or  gasoline  are  used,  the  fuel  cost  usually 
forms  the  major  part  of  the  operating  expenses.     But  where  the 
cheaper  fuels  are  used  or  the  plant  is  of  high  efficiency,  as  is  often 


554 


INTERNAL  COMBUSTION  ENGINES 


the  case  in  producer  plants,  an  analysis  will  show  that  what  are 
usually  considered  the  "  incidental"  expenses  in  many  cases  far 
outweigh  the  fuel  cost. 

The  fuel  cost  varies  with  the  load  on  the  engine.  The  figures 
given  by  manufacturers  usually  represent  the  best  figures  obtained 
at  maximum  load,  but  such  conditions  rarely  obtain  in  practice. 
At  any  rate  it  would  not  be  safe  to  base  computations  upon  such 
" parade"  figures.  Haeder  *  considers  that  the  economy  figure 
given  by  an  engine  at  T7^  maximum  load,  which  is  equal  to  85 
per  cent  of  rated  load  if  an  over-capacity  of  20  per  cent  is 
assumed,  is  the  best  figure  on  which  to  base  computations. 
The  same  writer  gives  the  following  table  for  the  variation  of  the 
fuel  consumption  with  load.  The  third  line  in  this  table  gives 
the  same  information  regarding  a  steam  plant: 


VARIATION  OF  FUEL  CONSUMPTION  WITH  LOAD 

Gas  Engine 

.1 

Max. 
Load 

.9 

.8 

.7 

.6 

.5 

.4 

.3 

.2 

of 
Max. 

Load 

Hit-and-miss  regulation 

1 

1.03 

1.08 

1.14 

1.23 

1.35 

1.50 

1.8 

2.5 

3.0 

Throttling  regulation    . 
Steam  plant  

1 
1.1 

1.06 
1.05 

1.13 
1.02 

1.21 
1.0 

1.33 
.96 

1.50 
1.02 

1.75 
1.07 

2.2 
1.15 

3.0 
1.30 

5.0 
1.60 

The  table  is  based  upon  the  assumption  that  the  gas  engine 
operates  normally  on  T7^  of  its  maximum  load,  and  this  is  put 
equal  to  the  normal  load  on  the  steam  engine.  It  is  interesting 
to  note  the  superiority  of  hit-and-miss  regulation,  as  far  as  econ- 
omy is  concerned,  over  the  other  method  of  governing,  and  the 
superiority  of  the  steam  engine  over  both  as  regards  small  varia- 
tion in  economy  over  a  wide  range  of  load. 

Gulderf  makes  a  similar  estimate  with  the  following  results: 

INCREASE  OF  FUEL  CONSUMPTION  WITH  DECREASING  LOAD 

Approximate  Load 75  .66  .50  .33 

Illuminating  Gas  Engine .      10  20  35  60 

Suction  Gas  Engine 20  30  50  75 

Diesel  Oil  Engine 10  20  30  55 


.25    of  Normal  Load. 
90  )  per  cent  higher  fuel 
100  >    consumption  than 
80  )    at  full  load. 


*  Haeder,  Die  Gasmotoren. 

f  Guldner,  Verbrennungsmotoren,  p.  427. 


COST  OF  INSTALLATION  AND  OF  OPERATION      555 

Thus,  for  example,  if  an  illuminating  gas  engine  uses  20  cu*  ft. 
of  gas  per  B.  H.  P.  hour  at  full  load,  we  may  except  it  to  use  1.35 
X  20  =  27  cu.  ft.  per  B.  H.  P.  hour  at  half  load,  and  1.9  X  20  = 
38  cu.  ft.  per  B.  H.  P.  hour  at  quarter  load. 

The  anthracite  coal  consumption  of  suction  gas  plants  for 
various  sizes  of  plants  and  for  different  loads  is  given  by  Haeder 
in  the  following  table: 

CONSUMPTION  OF  ANTHRACITE   IN  SUCTION  GAS  PLANTS  IN  POUNDS  PER 

B.  H.  P.-hour 


Max.  Capacity  B.  H.  P.  ... 

14 

40 

70 

100 

140 

210 

420 

Normal  Load  B.  H 

.P. 

10 

30 

50 

70 

100 

150 

300 

Consumption 
pounds  per 
H.  P.-hour 

B. 
.7B. 

H.P 
H.P 

•  max. 
•max. 

1.21 
1.45 

1.0 
1.19 

.93 
1.12 

1 

90 
10 

.88 
1.06 

.86 
1.03 

.84 
1.01 

based  on  .  . 

.5B. 

H.P 

•max. 

1.80 

1.47 

1.38 

1. 

34 

1.32 

1.28 

1.25 

It  is  evident  from  a  study  of  the  figures  in  the  above  tables 
that  the  probable  average  load  at  which  a  prospective  plant  will 
operate  plays  an  important  part  in  the  estimation  of  fuel  costs,  a 
point  which  should  not  be  lost  sight  of. 

We  find  in  the  engineering  literature  of  the  day  considerable 
information  regarding  fuel  consumption  and  fuel  costs.  The 
cost  figures  given  belong  to  one  of  two  classes:  either  they  are 
based  upon  assumptions  regarding  both  consumption  of  fuel  and 
cost  of  unit  weight  of  the  fuel,  or  the  figures  are  obtained  in 
actual  operation.  It  goes  without  saying  that  the  latter  class  is 
much  more  valuable  than  the  former.  In  the  case  of  assumed 
costs  and  consumptions,  comparisons  are  usually  made  between 
steam  and  gas  power  under  various  conditions  of  operation. 
Such  computations  are  interesting  because  they  show  what 
might  be  realized  in  each  case,  but  in  attempting  to  practically 
apply  the  information  the  greatest  attention  should  be  paid  to 
the  conditions  assumed.  As  regards  actual  consumption  figures, 
the  tables  of  the  previous  chapter  give  considerable  information 
regarding  efficiency  of  operation.  From  this  data  it  should  be 
easy  to  compute  the  fuel  costs  as  soon  as  the  local  cost  of  unit 
weight  is  known. 

Below  are  given  a  few  hypothetical  computations.     In  some 
cases  both  the  fuel  consumption  and  the  fuel  cost  are  assumed1 
outright,  in  others  an  attempt  has  been  made  to  determine  the 


556 


INTERNAL  COMBUSTION  ENGINES 


fuel  consumption  in  relation  to  the  size  of  the  engine.  These 
figures  are  followed  by  a  few  fuel  cost  figures  from  actual  practice. 
Additional  data  for  fuel  cost  from  actual  operation  will  be  found 
in  the  data  on  total  operating  costs  at  the  end  of  this  chapter. 

The  following  table  shows  an  estimate  taken  from  the  cata- 
logue of  a  well-known  manufacturer. 

RELATIVE  COSTS  OF  FUEL  WITH  DIFFERENT  TYPES  OF  ENGINES 


Type  of  Engine 

Class  of  Fuel 

Price  of  Fuel 

Fuel  Con- 
sumed per 
B.  H.  P. 
per 
hour 

Cost  in 
cents  per 
B.  H.  P. 
per 
hour 

Cost  per 
annum  3000 
hours  per 
100  B.  H.  P. 

Simple   n  on-  con- 
densing slide  valve 
Compound  con- 
densing   
Steam  Turbine  
Oil  Engine 

Bituminous  Coal 
Bituminous  Coal 

Bituminous  Coal 
Gasoline  

Crude  Oil  
IlluminatingGas 
Natural  Gas  .  .  . 
Anthracite  Coal 
Coke  

$3.00  per 
gross  ton 
$3.00 

$3.00 
14  cents  per 
gal. 
4  cents    per 
gal-, 
75  cents  per 
1000  cu.  ft. 
20  cents  per 
1000  cu.  ft. 
$3.00  per 
gross  ton 
$3.00  per 
gross  ton 

51bs. 
3  It*. 

3  Ibs. 
0.125  gal. 

0.10  gal. 
19  cu.  ft. 
13  cu.  ft. 
1  Ib. 
1.251b. 

.669 
.402 

.402 
1.75 

.40 
1.425 
.26 
.134 
.167 

$2,007.00 
1,205.00 

1,205.00 
5,250.00 

1,200.00 
4,275.00 
780.00 
402.00 
502.00 

Oil  Engine  

Gas  Engine.  .  .  

Gas  Engine 

Gas  Engine   with 
suction  producer.  . 
Gas   Engine   with 
suction  producer.  . 

The  next  table,  compiled  by  J.  I.  Wile,  is  similar  to  the  above, 
except  that  the  assumptions  differ  somewhat.  A  comparison  of 
the  corresponding  items  in  the  two  tables  serves  to  show  the 
variation  in  the  final  results  arrived  at  by  computations  of  this 
kind. 


COST  OF  INSTALLATION  AND  OF  OPERATION      557 


STATISTICS  OF  FUEL  CONSUMPTION   AND  COST  PER  ANNUM   OF   PRODUCER 
GAS  POWER  AND  OTHER  POWERS 


Type  of  Engine 

Kind  of 
Fuel 

Price  per 
Ton 

Fuel  consump- 
tion in  Ibs.  per 
B.  H.  P.  per 

Cost  in 
cents  per 
B.  H.  P. 

Cost  in 
dollars 
per  100 
B.  H.  P. 

Cost  per 
100B.H. 
P.  per 
Annum 

hour 

per 

per 

3000 

hour 

hour 

hours 

O 
P 

Oil  Engine 

Gasoline 

12  cents  per 

1  Pint 

1.50 

$1.50 

$4,500 

1 

Gallon 

i 

Gas  Engine 

Illuminating 

75c  per  1000 

18  Cubic  Feet 

1.35 

1.35 

4,050 

w 

Gas 

Cubic  Feet 

per  B.  H.  P. 

£ 

Gas  Engine  

Natural  Gas 

30c  per  1000 

13  Cubic  Feet 

.39 

.39 

1,170 

»-*- 

a 

Cubic  Feet 

per  B.  H.  P 

B 

Simple  Steam  Engine  .  .  . 

Bituminous 
Coal 

$3.00 

8  Ibs. 

1.2 

1.20 

3,600 

|V     C/3 
I 

Compound  Steam  Engine 
Non-condensing  

Bituminous 
Coal 

3.00 

5 

.75 

.75 

2,250 

3 

M 

Triple  Expanding  Steam 
Engine,  condensing  .  .  . 

Bituminous 
Coal 

3.00 

2 

.3 

.30 

900 

Producer  Gas  Engine  .  .  . 

Anthracite 

5.00 

1 

.25 

.25 

750 

1    "^ 

Coal 

3 

Producer  Gas  Engine  .  .  . 

Gas  Coke 

3.00 

1.25 

.1875 

18| 

565 

Producer  Gas  Engine  .  .  . 

Bituminous 

2.50 

1.25 

.1565 

!l565 

470 

0 

Coal 

!« 

Producer  Gas  Engine  .  .  . 

Anthracite 

3.00 

1 

.15 

.15 

450 

E? 

Coal 

1  £ 

C.  H.  Day,*  in  an  investigation  on  the  economy  of  gas  pro- 
ducer engines,  compiled  the  following  fuel  cost  data  for  the 
various  kinds  of  prime  movers  mentioned.  The  fuel  consump- 
tion figures  were  obtained  in  each  case  by  collaborating  the 
results  of  a  considerable  number  of  tests.  The  costs  per  annum 
were  then  computed  by  assuming  the  cost  of  unit,  weight  of  the 
fuel.  The  total  time  of  operation  per  year  is  taken  at  3000 
hours. 

ANNUAL  FUEL  COSTS  FOR  STEAM  ENGINES.     COST  OF  COAL  ASSUMED  AT 
$3.00  PER. TON  OF  2000  LBS. 


Type  of  Engine 

B.  H.  P. 

Lbs.  Coal  per  B.  H.  P. 
per  hour 

Cost  of  Coal  per  B.  H. 
P.  per  year 

Simple,  non-condensing  
Simple,  condensing  
Compound,  condensing    
Compound,  condensing    
Compound,  condensing    
Triple  exp.  condensing     

50 
100 
200 
600 
1000 
2000 

5.75 
4.45 
2.74 
1.97 
1.90 
1.87 

$25.90 
20.00 
12.70 

8.85 
8.55       , 
8.40 

The  data  available  for  steam  turbines  is  not  as  extensive  as 
*Sibley  College  Thesis,  1905. 


558 


INTERNAL  COMBUSTION  ENGINES 


that  for  steam  engines,  and  the  range  covered  is  not  so  wide  as 
regards  capacity.  The  following-  figures,  also  compiled  by  Mr. 
Day,  show  some  fuel  costs  for  prime  movers  of  this  kind.  The 
working  time  has  again  been  assumed  at  3000  hours  per  annum. 

ANNUAL  FUEL  COSTS  FOR  STEAM  TURBINES.     COST  OF  COAL  ASSUMED  AT 
$3.00  PER  TON  OF  2000  LBS. 


Number  of  Tests 

Average  B.  H.  P. 

Lbs.  Coal  per 
B.  H.  P.-hour 

Cost  of  Coal  per  B.  H.  P. 
per  year 

27 

10 
5 
25 

616 
1085 
1359 
1739 

1.740 

1.735 
1.725 
1.655 

$7.83 
7.80 
7.75 
7.44 

The  computations  made  on  illuminating  and  natural  gas 
engines  show  the  following  results.  Time  of  operation  per  year 
3000  hours,  cost  of  illuminating  gas  75  cents  per  1000  cu.  ft.,  cost 
of  natural  gas  50  cents  per  1000  cu.  ft.  The  latter  assumption 
is  high,  since  in  many  localities  natural  gas  is  sold  at  30  or  even 
20  cents  per  1000  cu.  ft.  It  is  a  simple  matter,  however,  to  reduce 
the  figures  in  the  table  in  the  corresponding  ratio. 

ANNUAL  FUEL  COST  FOR  ILLUMINATING  AND  NATURAL  GAS  ENGINES.  COST 
OF  ILLUMINATING  GAS  ASSUMED  AT  75  CENTS,  THAT  OF  NATURAL  GAS 
AT  50  CENTS,  PER  1000  CU.  FT. 


Cu.  ft.  per  B.  H.  P.-hour 

Annual  Cost  of  Gas  per  B.  H.  P.  per  year 
of  3000  hours 

B.  H.  P. 

Illuminating 
Gas 

Natural 
Gas 

Illuminating 
Gas  Engines 

Natural  Gas 
Engines 

10 

22.0 

$49.50 

$24.00 

20 

21.5 

16.0 

48.30 

23.50 

30 

21.0 

15.5 

47.20 

23.30 

40 

20.5 

15.0 

46.00 

22.60 

50 

20.0 

14.5 

44.80 

21.80 

75 

19.1 

13.8 

42.80 

20.80 

100 

18.3 

13.0 

41.10 

19.60 

200 

— 

11.4 



17.10 

300 

— 

10.2 



15.40 

400 

— 

9.7 



14.60 

500 

9.4 

— 

14.10 

COST  OF  INSTALLATION  AND  OF  OPERATION      559 


For  producer  gas  engines  Day  found  the  following  figures  for 
the  consumption  of  gas  and  of  coal,  from  which  the  fuel  costs  per 
year  of  3000  hours  are  computed,  assuming  coal  to  cost  $4  per 
ton  of  2000  pounds. 

ANNUAL  FUEL  COST  OF  PRODUCER  GAS  ENGINES 


B.  H.  P. 

Cu.  ft.  of  Gas 
per  B.  H.  P.-hour 

Lbs.  of  Coal 
per  B.  H.  P.-hour 

Annual  Cost  of  Coal 
per  B.  H.  P. 

50 

105 

.45 

$8.70 

100 

96 

.35 

8.10 

150 

89 

.23 

7.33 

200 

83 

.17 

7.03 

250 

79 

.12 

6.72 

300 

76 

1.08 

6.48 

400 

73 

1.05 

6.30 

500 

72 

1.03 

6.18 

.  The  cost  of  the  gas  for  blast  furnace  gas  engines  has  in  many 
computations  been  neglected  on  the  assumption  that  this  gas, 
if  not  used  in  engines,  is  a  mere  waste  product.  Lately,  however, 
it  has  come  to  be  recognized  that  some  value  must  be  assigned  to 
this  fuel  since  money  was  expended  on  it  in  every. case  for  clean- 
ing it  preparatory  to  making  it  fit  for  use  in  engines.  The  ordinary 
method  of  evaluating  this  gas  is  to  compare  its  heat  content  with 
that  of  steam  and  to  assign  a  value  to  the  gas  corresponding  to 
the  cost  of  steam.  Thus  the  cost  of  the  gas  will  in  every  locality 
vary  with  the  cost  of  coal.  As  an  example,  H.  Freyn  *  makes 
the  following  computation: 

"Let  us  assume  that  the  price  of  coal  delivered  into  bins  at 
the  plant  be  $2.75  per  ton,  that  the  coal  have  a  heat  value  of 
13,000  B.  T.  U.  per  pound,  and,  further,  that  steam  of  150  pounds 
boiler  pressure  or  about  165  pounds  absolute  pressure  be  raised 
by  burning  this  coal  under  boilers.  One  pound  of  steam  will 
then  contain  1225  B.  T.  U.  from  zero  degrees  Fahrenheit.  Assum- 
ing feed  water  at  70  degrees,  there  would  be  required  1 155  B.  T.  U. 
to  generate  1  pound  of  steam  at  150  pounds  boiler  pressure.  In  a 
boiler  plant  having  65  per  cent  efficiency,  1000  pounds  of  coal 

*  H.  Freyn,  Available  Power  and  Cost  of  Operation  of  a,  Power  Station 
for  Waste  Gases  from  a  Blast-furnace  Plant.  Journal  Western  Society  of 
Engineers,  February,  1906. 


560  INTERNAL  COMBUSTION  ENGINES 

could  raise  (0.65  X  1000  X  13,000)  -i-  1155  =  7300  pounds  of 
steam.  The  value  of  1000  pounds  of  steam  would  be  2.75  -r- 
(2  X  7.3)  .=  $0.188,  or  18.8  c.  To  this  must  be  added  for  labor 
and  maintenance  approximately  1  c.  per  1000  pounds  of  steam, 
making  the  total  value  of  1000  pounds  =  19.8  c.  1000  cu.  ft.  of 
blast  furnace  gas  have  a  heat  value  of  1000  X  90  =  90,000  B.  T.  U. 
and  are  equivalent  to  (0.65  X  90,000)  H-  1155  =  51  pounds  of 
steam,  which  in  turn  are  worth  (51  -r-  1000)  X  19.8  =  1  c. 

"The  value  of  1000  cu.  ft.  of  blast  furnace  gas  would,  therefore, 
be  1  c." 

L.  Eberhardt,  in  an  article  in  the  Zeitschrift  d.  V.  d.  I,*  makes 
a  similar  computation,  arriving  at  a  somewhat  different  result. 
Starting  with  the  assumption  that  1000  pounds  of  steam  will 
cost  from  25  to  32  c.,  according  to  the  price  and  quality  of  coal, 
he  finds  that  1000  cu.  ft.  of  cleaned  blast  furnace  gas  should  have  a 
value  of  from  1.43  to  1.84  c.,  the  gas  having  a  heating  value  of  102 
B.  T.  U.  per  cu.  ft.  This  is  considerably  higher  than  the  value 
found  by  Freyn,  which  is  mainly  due  to  the  lower  grade  of  coal 
(11,650  B.  T.  U.  per  pound)  and  the  higher  grade  of  gas  assumed. 

To  get  some  idea  of  the  fuel  cost  of  blast  furnace  gas  power 
as  compared  with  steam  power,  Eberhardt,  in  the  article  men- 
tioned, gives  the  following  tables.  The  original  tables  give  the 
cost  per  B.  H.  P.  hour,  but  these  have  been  recomputed  to  the 
basis  of  a  year  of  3000  working  hours,  to  make  them  directly  com- 
parable with  the  figures  in  previous  tables. 

ANNUAL  FUEL  COST  OF  BLAST-FURNACE  GAS  ENGINES.  HEATING  VALUE 
OF  COAL  TAKEN  AT  11650  B.  T.  U.  PER  LB.  HEATING  VALUE  OF  GAS 
TAKEN  AT  102  B.  T.  U.  PER  cu.  FT. 

Cost  of  coal  per  ton  of  2000  Ibs dollars  2.34  2.75  3.18 

Cost  of  1000  Ibs.  of  steam    cents  24.8  28.4  31.8 

Cost  of  1000  cu.  ft.  of  gas cents  1.43  1.64  1.84 

A  fair  blast  furnace  gas  engine  will  show  the  following  fuel 
consumption : 

At  full  load    99  cu.  ft.  of  gas  per  B.  H.  P.  hour. 

At  T9^  load   106          "               "  " 

At  T\  load   113          "               "  « 

At  §  load      122          "               "  « 
At  i  load      131          "               " 

*  June  3,  1905. 


COST  OF  INSTALLATION  AND  OF  OPERATION      561 

With  these  assumptions  of  gas  consumption  per  B.  H.  P.,  and 
of  local  cost  of  coal,  the  fuel  costs  per  B.  H.  P.  per  year  of  3000 
hours  will  then  be  as  per  the  following  table: 


Cost  of 
Coal 
per  Ton 

Per  Cent  full  Load  on  Engine 

100 

90 

80 

66 

50 

Annual  Cost  of  Blast  Furnace  Gas  per  B.  H.  P.    Dollars 

$2.34 

2.75 
3.18 

4.26 

4.85 
5.46 

4.56 
5.18 
5.83 

4.87 
5.55 
6.23 

5.25 
5.97 
6.72 

5.63 
6.42 
7.20 

The  fuel  cost  of  operating  on  gasoline  as  fuel  is  of  course  con- 
siderably higher  than  any  of  the  figures  above  quoted.  The  usual 
assumption  made  in  regard  to  gasoline  engines  is  that  they  will 
require  1  pint  of  gasoline  per  B.  H.  P.  hour.  This  corresponds 
to  a  thermal  efficiency  of  about  18  per  cent  on  the  brake,  a  figure 
which  should  be  reached  by  a  fair-sized  engine  in  good  condition. 
For  the  smaller  machines,  however,  one  pint  is  perhaps  some- 
what low,  and  for  say  a  2  horse-power  machine  a  consumption  of 
2  pints  per  B.  H.  P.  hour  is  probably  a  safer  assumption.  It 
should  also  be  borne  in  mind  that  the  purchase  price  of  gasoline 
varies  somewhat  with  the  quantity  bought.  The  following  table 
of  fuel  costs  takes  these  various  points  into  account. 

FUEL  COST  FOR  GASOLINE  ENGINES  PER  B.  H.  P.  PER  YEAR  OF  3000  WORKING 

HOURS 

Size  of  Engine,  B.  H.  P 2  4  6  10  20 

Cost  of  gasoline  per  gal.,  cents 20  18  16  14  13 

Consumption  of  gasoline  per  B.  H.  P. 

hr.,  gallons    25  .20  .18  .15  .12 

Fuel  cost  per  B.  H.  P.  per  year,  dollars  150.00  108.00  86.40  63.00  46.80 

(e)  COST  OF  WATER  FOR  COOLING  AND  WASHING.  Many  esti- 
mates of  total  operating  costs  totally  neglect  the  cost  of  water 
for  cooling  and  washing  purposes  required  by  the  plant,  although 
in  many  localities  this  may  amount  to  a  considerable  item  of 
expense.  In  general  terms,  where  water  has  to  be  brought  from 
city  mains,  it  pays  to  install  cooling  apparatus  of  some  kind. 
Of  course  for  small  installations  this  may  be  simply  a  tank  from 


562  INTERNAL  COMBUSTION  ENGINES 

the  surface  of  which  the  heat  is  radiated.  The  tank  is  connected 
at  top  and  bottom  with  the  water  jacket  of  the  engine,  and  the 
water  circulates  by  convection.  Where  such  a  cooling  tank  can- 
not be  placed  in  the  immediate  vicinity  of  the  engine,  and  con- 
nected to  the  jacket  by  short  straight  pipes,  a  circulating  pump 
of  some  kind  must  be  used.  As  the  size  of  the  installation  grows, 
cooling  towers  or  cooling  ponds  have  to  be  resorted  to,  unless  an 
abundant  source  of  clean  water  is  available  without  cost,  except 
that  of  pumping.  Under  such  conditions  the  cost  of  cooling 
water  is  very  materially  reduced.  With  any  kind  of  cooling 
system  the  cost  then  consists  of  the  cost  of  pumping  plus  the  cost 
of  any  clean  water  that  must  be  supplied  from  time  to  time  to 
replace  that  lost  by  evaporation.  Of  course  it  is  not  possible  to 
give  any  definite  figures  for  this  cost  item,  because  it  depends 
upon  the  cost  of  water  in  the  particular  locality,  upon  the  total 
amount  of  water  circulated,  and  upon  the  kind  of  pumps  used. 
A  few  figures  for  the  amount  of  water  required  or  in  circulation 
per  B.  H.  P.  hour  are  given  below. 

In  a  producer  plant  an  additional  amount  of  water  is  required 
for  the  producers  and  scrubbers.  The  water  vaporized  for  the 
producers  of  course  is  not  again  available.  That  used  for  the 
washing  plant  is  in  general  subject  to  the  same  considerations  as 
that  used  for  cooling  the  engines.  But  where  a  cooling  system  is 
used  for  both,  they  should  never  be  combined,  because  the  re- 
quirements for  clean  cooling  water  for  the  engines  are  much  more 
strict.  The  scrubber  water  usually  carries  considerable  quantities 
of  sediment  and  is  contaminated  with  ammonia  and  sulfur  com- 
pounds, so  strongly  in  some  cases  as  to  give  it  a  very  noxious 
odor.  In  such  cases,  settling  tanks  and  ponds,  together  with  a 
considerable  addition  of  clean  water,  seem  to  be  the  only  remedies 
to  recover  at  least  a  part  of  the  water. 

The  approximate  quantity  of  cooling  water  required  may  be 
figured  from  the  following  considerations: 

One  horse-power,  assuming  an  engine  efficiency  of  say  25  per 

cent  at  the  cylinder,  requires  the  expenditure  of  —  -   =  10,200 

.25 

B.  T.  U.  per  I.  H.  P.  hour.  The  jacket  loss  approximates  about 
40  per  cent  of  the  heat  expended,  that  is,  in  this  case  the  jacket 
water  must  carry  off  .40  X  10,200  =  4080  B.  T.  U.  per  hour. 


COST  OF  INSTALLATION  AND  OF  OPERATION      563 


Assuming  the  inlet  temperature  at  70  degrees,  the  outlet  at  150 
degrees,  we    find    the   number  of  pounds    of  water  required  = 

4080 

approx.  — - — — -  =51  pounds  =say  6£  gallons  per  I.  H.  P.  hour 
1  oU  —  7  u 

at  full  load. 

The  following  figures  from  various  sources  show  how  this 
estimate  agrees  with  others  and  with  some  data  from  actual 
practice. 

W.  Heym,  in  the  Gasmotorentechnik*  states  that  a  producer 
plant  requires  per  horse-power  hour  6.5  gallons  for  the  engine, 
4  gallons  for  the  scrubber,  and  .13  gallons  for  the  producer  vapo- 
rizer. 

Freyn,  in  the  paper  already  mentioned,  makes  the  following 
estimates  for  a  blast  furnace  gas  plant  of  10,500  B.  H.  P.  Theissen 
washers  are  used  to  clean  the  gas. 

GALLONS  OF  COOLING  WATER  REQUIRED 


Ixxul  on  Engines 

For  the  Engines  per  B.  H.  P.-hour 

For  the  Washers  per  1000 
cu.  ft.  of  gas  cleaned 
per  minute 

Full 
I 

8.5 
10.5 
13.0 

12.0 
14.0 
16.0 

Freyn  also  estimates  that  if  the  plant  is  located  near  a  stream 
of  water,  the  cost  of  pumping  would  probably  be  in  the  neighbor- 
hood of  2  c.  per  1000  gallons. 

J.  R.  Bibbins  f  on  a  51-hour  test  of  a  500  horse-power  Westing- 
house  horizontal  engine,  reported  a  water  consumption  for  the 
engines  only  of  9.4  gallons  per  B.  H.  P.  hour  at  full  load.  The 
same  authority  reports  a  figure  of  5.65  gallons  per  B.  H.  P.  hourt 
found  on  similiar  engines  in  another  plant. 

In  conclusion  it  should  be  said  that  the  water-consumption 
of  gas  engines  depends  somewhat  upon  the  size  of  the  cylinder. 
Thus  a  single-acting  cylinder  of  very  large  diameter  usually 

*  November,  1907. 

f  J.  R.  Bibbins,  Proceedings  A.  S.  M.  E.,  Mid-November,  1907. 
t  J.  R.  Bibbins,  Gas  Driven  Electric  Power  Station,Proc.  of  the  Eng.  Soc. 
of  W.  Pa. 


564  INTERNAL  COMBUSTION  ENGINES 

requires  more  cooling  water  than  two  single-acting  or  one  double- 
acting  cylinder  of  the  same  capacity.  Skilful  attendance  also 
is  a  considerable  factor  in  the  amount  of  cooling  water  used,  a 
point  which  is  very  often  neglected. 

(/)  OIL  AND  WASTE.  The  consumption  of  lubricating  oil  per 
B.  H.  P.  hour  depends  upon  the  size  of  the  engine  and,  as  in  the 
case  of  cooling  water,  largely  also  upon  the  care  of  attendants. 
It  is  also  true  that  new  machines  may  for  a  time  require  two  or 
three  times  the  ordinary  amount  of  oil  until  all  the  parts  have 
become  adjusted  to  their  service.  In  large  and  medium  sized 
plants  it  is  usual  to  employ  a  gravity  or  circulating  system  of 
oiling,  in  which  case  the  oil  is  recovered,  filtered,  and  again  used. 
In  such  systems  the  cost  of  oil  is  a  small  item  and  consists  mostly 
of  the  cost  of  oil  necessary  to  replace  that  unavoidably  lost.  Of 
course  none  of  the  cylinder  oil  used  is  recovered. 

Giildner  estimates  that  the  consumption  of  lubricating  oil 
usually  varies  from  .006  to  .008  pints  of  oil  per  B.  H.  P.-hour,  and 
that  under  favorable  conditions  .003  pints  per  B.  H.  P.-hour  may 
be  reached.  L.  L.  Brewer  finds  that  the  consumption  for  the  large 
engines  quoted  in  the  table,  page  552,  varies  from  .0045  to  .0055 
pints  per  B.  H.  P.-hour,  and  that  in  double-acting  two-cycle 
engines  the  consumption  may  be  as  low  as  .0035  pints. 

The  following  table  compiled  by  J.  R.  Bibbins  and  published 
in  the  paper  before  the  Society  of  Engineers  of  West  Pennsylvania, 
already  quoted,  shows  the  actual  oil  consumption  in  a  plant  con- 
taining two  horizontal  Westinghouse  engines  of  500  horse-power 
each,  direct  connected  to  300  K.  W.  generators.  The  figures 
cover  a  period  of  four  months  and  the  results  should  therefore  be 
very  reliable,  -  The  system  of  oiling  used  is  of  the  continuous 
circulating  and  filtering  type.  The  consumption  amounts  to 
.00202  pints  of  cylinder  oil  and  .00286  pints  of  engine  oil  per 
horse-power  hour,  which  agrees  well  with  the  figures  given  by 
Brewer. 


COST  OF  INSTALLATION  AND  OF  OPERATION      565 

OIL  CONSUMPTION 
4  months  ending  Sunday,  May  23,  1906 

CYLINDER  OIL  *  ENGINE  OIL  f 

Kind Imperial  Cylinder  Oil  Special  Gas  Engine  Oil 

Maker   Union  Petroleum  Co.,  Philadelphia 

Price  (barrel  lots)    32  cents  per  Gal.  18  cents  per  Gal. 

Quantity  used 561  Gals.  765  Gals. 

Quantity  used  per  month 140£  Gals.  191J  Gals. 

Quantity  used  per  (opertg.)  day  .  .  .     4.68  Gals.  6.38  Gals. 

Quantity  used  per  full  day    6.07  Gals.  8.27  Gals. 

Engine  Hours  per  day 37  37 

Engine  H.P.  Hours  per  day 18500  18500 

Oil  per  Engine  Hour 0.127  Gals.  0.172  Gals. 

Oil  per  H.P.  Hour 0.000253  Gals.  0.000345  Gals. 

Cost  per  Engine  Hour 4.05  cents  3.1  cents. 

Cost  per  H.P.  Hour 0.00809  0.00621 

Total  Cost 0.0143  cents  per  H.P.  Hour 

The  cost  of  cotton  waste  or  other  cleaning  material  is  an  item 
very  hard  to  estimate,  and  in  any  case  of  little  influence  on  the 
final  result.  It  is  usually  combined  with  the  cost  of  oil,  and 
some  figures  for  this  combined  cost  will  be  found  in  the  estimates 
of  total  operating  costs  at  the  end  of  this  chapter. 

(g)  ATTENDANCE.  The  statement  very  often  carelessly  made 
with  regard  to  small  gas  engine  installations,  that  they  require  no 
waiting  on,  is  of  course  not  quite  the  truth.  The  fact  is  that  a 
small  gas  or  gasoline  engine,  if  in  good  order,  does  not  require, 
after  starting,  much  attending  except  the  proper  handling  of  the 
lubricators.  In  this  respect  the  gas  power  installation  has  an 
advantage  over  the  small  steam  power  plant,  where  at  least  one 
man  is  generally  required  all  the  time.  For  small  natural  gas  or 
illuminating  gas  engines,  therefore,  it  is  possible  to  employ  the 
"  engineer,"  to  use  a  familiar  term,  somewhere  else  at  least  part 
of  the  time,  but  naturally,  as  the  size  of  engine  increases,  this 
spare  time  decreases,  and  it  is  doubtful  if  suction  gas  plants,  no 
matter  how  small,  can  get  along  with  less  than  one  man's  entire 
time. 

The  general  methods  of  taking  care  of  medium  sized  and  large 

*  Includes  crank  case  oil  for  exciter  engines.  Drainage  from  glands  of 
main  engines  collected,  mixed  with  old  engine  oil  and  used  in  crank  case.  No 
crank  case  oil  purchased. 

f  Includes  oil  consumption  o.f  auxiliaries.  Sufficient  quantity  old  engine 
oil  drawn  from  circulating  system  to  supply  auxiliaries  replaced  by  fresh  oil. 


566  INTERNAL  COMBUSTION  ENGINES 

gas  engines  are  perhaps  not  far  different  from  those  used  in  steam 
engine  practice.  It  cannot  be  denied,  however,  that  gas  engines 
have  much  more  opportunity,  so  so  speak,  to  go  wrong.  That  is, 
jacket  water,  lubrication,  igniters,  valves,  etc.,  all  need  careful 
looking  after,  and  any  of  these  things,  if  neglected,  may  cause 
a  shut  down.  While,  therefore,  steam  engine  attendants  generally 
accustom  themselves  to  the  new  service  very  quickly,  it  would  be 
wrong  to  assume  that  they  can  in  general  take  care  of  a  gas 
engine  plant  without  some  instruction  and  practice.  Of  course 
the  larger  the  plant,  the  more  important  this  point  becomes. 

There  seems  to  be  nothing  in  English  engineering  literature 
to  give  an  approximate  idea  of  the  time  actually  required  in 
attending  gas  engines.     Giildner  proposes  the  following  equations, 
apparently  based  on  practical  experience: 
For  illuminating  gas,  natural  gas  and  oil  engines, 

n  hours. 


For  suction  gas  plants   W  =  1.25  vA/»  hours 

where  W  =  time  of  attendance  required  in  hours  per  day  of  10 

hours  and  Nn  =  rated  capacity  of  plant. 

Thus,  for  instance,  a  100  horse-power  natural  gas  engine  would 
actually  require  about  .25  V  100  =  2.5  hours  in  a  10-hour  shift. 
Hence  the  attendant's  time  could  be  largely  used  somewhere  else. 
On  the  other  hand,  a  100  horse-power  suction  gas  plant  would 
actually  require  1.25  V  100  =  12.5  hours,  which  means  that  two 
men  will  have  to  be  employed. 

Where  a  station  is  made  up  of  several  smaller  units  and  pro- 
ducers, the  cost  of  attendance  naturally  increases.  Thus  if  there 
are  n  units  in  a  plant  of  Nn  horse-power  total,  Giildner  states  that 
the  actual  time  required  per  operating  day  of  the  plant  may  be 
expressed  by 

W  =  1.25  VnAT  hours. 

Thus  if  we  take  a  1200  horse-power  suction  gas  plant  made 
up  of  4  units  of  300  horse-power  each, 

W  «  1.25  V4  x  1200  =  86.5  hours, 
which  would  mean  the  service  of  9  men  in  the  10-hour  shift.     If 


COST  OF  INSTALLATION  AND  OF  OPERATION      567 

this  capacity  had  been  put  in  one  unit,  the  time  would  have  been 
W  =  1.25  VT200  =  43.5  hours, 

which  would  have  called  for  only  5  men  per  shift. 

If  in  any  of  the  above  equations  we  introduce  the  hourly  wage 
scale,  we  may  express  the  cost  of  attendance  per  B.  H.  P.  per 
hour.  Thus  if  the  scale  should  be  20  c.  per  hour,  we  would  have  for 
illuminating  gas,  natural  gas,  or  oil  engines,  for  the  10-hour  shift, 

Cost  per  B.  H.  P.-hour  -  20  X  . 


10  N 
For  suction  gas  plants, 


Cost  per  B.  H.  P.-hour  =  20  X  1.25         »  =  _^ 

10  Nn  VNn 

and  for  large  suction  gas  plants  of  n  units, 

Cost  per  B.  H.  P.-hour  -^Xi^  cents. 


There  is  little  data  available  to  check  the  accuracy  of  these 
formulae,  but  the  two  or  three  instances  cited  by  various  authori- 
ties for  the  labor  cost  in  suction  gas  plants  check  very  well  with 
the  results  of  the  formula. 

(h)  MAINTENANCE  AND  REPAIRS.  The  expenditures  for 
maintenance  and  repairs  of  a  gas  engine  installation  should  not 
exceed  3  per  cent  of  the  purchase  price  of  the  engines  and  pro- 
ducers. There  is  no  doubt  that  this  item  may  easily  run  to  10 
per  cent  and  over,  especially  if  in  a  producer  plant  insufficient 
attention  is  paid  to  cleaning  the  gas.  But  such  conditions  are 
not  normal  and  should  not  occur  in  good  practice. 

Freyn  states  that  the  following  are  average  figures  for  repair 
accounts  for  a  blast  furnace  gas  station  : 

2£  per  cent  per  year  of  the  price  of  the  engines  and  electric 
generators. 

7  per  cent  per  year  of  the  price  of  the  cleaning  plant. 

5  per  cent  per  year  of  the  price  of  the  air  compressor  used  for 
starting. 

2  per  cent  per  year  of  the  price  of  piping,  etc. 

To  this  may  be  added  from  1  to  2  per  cent  of  the  cost  of  the 
building  as  maintenance  for  the  building. 


568  INTERNAL  COMBUSTION  ENGINES 

Total  Operating  Costs  and  Cost  as  Compared  with  other 
Prime  Movers  —  As  in  the  case  of  fuel  costs,  the  information 
available  in  engineering  literature  on  total  operating  costs  is  of 
two  kinds.  In  the  first  kind  the  estimates  are  based  entirely 
upon  hypothetical  assumptions,  in  the  second  the  results  are 
those  obtained  in  actual  operation.  Again,  the  latter  informa- 
tion is  of  course  of  much  greater  value,  but  except  for  large  in- 
stallations little  of  this  class  has  been  made  public.  Especially 
as  regards  small  installations  of  gasoline,  oil  and  illuminating  gas 
engines  there  seems  to  be  an  almost  absolute  lack  of  data  referring 
to  total  operating  costs.  For  that  reason,  in  order  to  get  some 
idea  of  costs,  it  will  be  necessary  for  the  time  being  to  depend  upon 
cost  computations  based  on  assumptions.  In  any  concrete  case 
these  assumptions  should  be  carefully  scanned  to  see  how  they 
agree  with  actually  existing  conditions  before  forming  a  final  idea 
of  operating  cost. 

The  data  available  from  actual  practice  is  mainly  due  to  Mr. 
J.  R.  Bibbins  *  and  others,  of  the  Westinghouse  Machine  Com- 
pany, and  of  course  relates  to  Westinghouse  engines.  This,  how- 
ever, does  not  preclude  their  applicability  to  other  similar  plants. 
This  information,  combined  with  that  from  a  few  English  plants, 
is  about  all  that  can  be  cited  at  the  present  writing. 

Hypothetical  computations  are  nearly  all  made  on  a  compara- 
tive basis.  Of -this  kind  are  the  tables  published  by  W.  O.  Webber 
in  the  Engineering  News,  August  15,  1907.  It  is  not  easy  to  give 
a  concise  abstract  of  the  various  factors  assumed  in  the  compu- 
tation of  these  tables,  and  for  that  reason  they  are  given  in  full, 
except  for  electric  power  which  does  not  especially  interest  us  here. 

*  The  following  is  a  partial  list  of  the  valuable  papers  published : 
J.  R.  Bibbins,  Gas  Driven  Electric  Power  Systems,  Warren  &  Jamestown 
Street  Railway,  Eng.  Soc.  of  W.  Pa.;  Gas  Power  for  Central  Stations,  Am. 
Inst.  of  E.  E.,  New  York,  December  18,  1903;  Producer  Gas  Power  Plant, 
Proc.  A.  S.  M.  E.,  December,  1906;  Application  of  Gas  Power  to  Central 
Station  Work,  National  Elec.  Light  Assoc.,  Washington,  D.  C.,  June,  1907; 
Duty  Test  on  Gas  Power  Plant,  Proc.  A.  S.  M.  E.,  Mid-November,  1907; 
and  A.  West,  Gas  Power  in  Electric  Railway  Work,  American  Street  & 
Interurban  Railway  Assoc.,  Philadelphia  Convention,  1905. 

E.  E.  Arnold,  The  High  Power  Internal  Combustion  Engine  and  its  Fit- 
ness for  Central  Station  Work,  New  England  Street  Railway  Club,  March,  1904. 
Reprint  from  Power,  December,  1903,  A  Gas  Engine  Pumping  Station. 


COST  OF  INSTALLATION  AND  OF  OPERATION      569 


COST  OF  GASOLINE  POWER 

Size  of  plant  in  H.P 2 

Price  of  engine  in  place $150.00 

Gasoline  per  B.  H.  P.  per  hour. .  £  gal. 

Cost  per  gallon $0.22 

=  cost  per  3,080  hours $451.53 

Attendance  at  $1  per  day 308.00 

Interest,  5  per  cent 7.50 

Depreciation,  5  per  cent 7.50 

Repairs,  10  per  cent    15.00 

Supplies,  20  per  cent 30.00 

Insurance,  2  per  cent    3.00 

Taxes,  1  per  cent 1.50 

Power  cost $824.03       $1,371.75       $1,498.13       $2~01&50 

To  these  figures  should  be  added  charges  on  space  occupied  as  follows: 
Value  of  space  occupied $100.00          $150.00          $200.00          $300.00 

Interest,  5  per  cent $5.00 

Repairs,  2  per  cent    2.00 

Insurance,  1  per  cent    1.00 

Taxes,  1  per  cent 1.00 

Total  annual  charge  for  space     $9.00 

Total  cost  per  annum $833.03 

Cost  of  1  H.P.  per  annum,  10 

hour  basis 416.51 

Cost  of  1  H.P.  per  hour    $0.1352 


6 
$325.00 

igal. 
$0.20 

10 

$500.00 

fgai. 

$0.19 

20 
$750.00 

igal. 
$0.18 

$924.00 

308.00 
16.25 
16.25 
32.50 
65.00 
6.50 
3.25 

$975.13 

308.00 
25.00 
25.00 
50.00 
100.00 
10.00 
5.00 

$1,386.00 

308.00 
37.50 
37.50 
75.00 
150.00 
15.00 
7.50 

$7.50 
3.00 
1.50 
1.50 

$10.00 
4.00 
2.00 
2.00 

$15.00 
6.00 
3.00 
3.00 

$13.50 

$18.00 

$27.00 

$1,385.25 

$1,516.13 

$2,043.30 

239.87 
$0.0780 

151.61 
$0.0492 

102.17 
$0.0331 

COST  OF  GAS  POWER 

$1.50  per  1000  cubic  feet  of  gas  less  20  per  cent, 'if  paid  in  10  days  =  $1.20 
net,  gas  760  B.  T.  U. 

Size  of  plant  in  H.P 2  6  10  20 

Engine  cost  in  place $200.00          $375.00 


$550.00       $1,050.00 


Gas  per  H.P. -hour  in  cubic  feet.     30 


Value  of  gas  consumed,   3080 

hours 

Attendance,  $1  per  day    

Interest,  5  per  cent 

Depreciation,  5  per  cent 

Repairs,  10  per  cent    

Supplies,  20  per  cent 

Insurance,  2  per  cent    

rri i     


$221.76 
308.00 
10.00 
10.00 
20.00 
40.00 
4.00 
2.00 

$615.76 
Annual  charge  for  space 9.00 

Total  cost  per  annum $624.76 

Cost  of  1  H.P.  per  annum,   10 

hour  basis 312.38 

Cost  of  1  H.P.  per  hour $0.1014 


Insurance,  2  per  cent 
Taxes,  1  per  cent  . 

Power  cost 


25 


$554.40 

308.00 

18.75 

18.75 

37.50 

75.00 

7.50 

3.75 

$1,023.65 
13.50 


172.86 
$0.0561 


22 


$843.12 

308.00 

27.50 

27.50 

55.00 

110.00 

11.00 

5.50 

$1,387.62 
18.00 


110.56 
$0.0456 


20 

$1,478.00 

308.00 

52.50 

52.50 

105.00 

210.00 

21.00 

10.50 

$2,237.50 
27.00 


$1,037.15       $1,405.62       $2,264.50 


143.22 
$003.67 


570 


INTERNAL  COMBUSTION  ENGINES 


COST  OF  STEAM  POWER 

Size  of  plant  in  H.P 6 

Cost  of  plant  per  H.P .  $250.00 

Fixed  charge,  14  per  cent $35.00 

Coal  per  H.P.-hour,  in  pounds 20 

Cost  of  coal  at  $5  per  ton $1512? 

Attendance,  3080  hours    75.00 

Oil,  waste  and  supplies lo.OU 

Cost  1  H.P.  per  annum,  10-hour  basis $279.00 

Cost  of  1  H.P.  per  hour    $0.0906 


10 


20 


$220.00 

$30.80 

15 

$103.00 
50.00 
10.00 

$194.80 
$0.0832 


$200.00 

$28.00 
12 

$82.50 

30.00 

6.00 

$146.50 
$0.0475 


ANNUAL  COST  OF  POWER  PER  BRAKE  HORSE-POWER  * 


B.  H.  P.  of  Unit 


1                         $600.00 

500.00 

3  "                                 437.50 

4  '  375.00 

5  '  320.00 

6  '  280.00 

7                                    250.00 

8                                      230.00 

9                          210.00 

10                  195.00 

12 175.00 

14 165.00 

16 157.50 

18 : 150.00 

20 146.00 

22 140.00 

24 137.50 

26 133.00 

28    130.00 

30 127.50 

35 124.00 

40 120.00 

50 112.50 

60 105.00 

70 100.00 

80 95.00 

90 90.50 

100 86.40 


Steam 


Gas 


$380.00 

312.50 

260.00 

220.00 

192.50 

172.50 

160.00 

152.50 

145.00 

140.00 

132.50 

126.00 

120.00 

116.50 

113.00 

110.00 

107.50 

105.00 

102.50 

102.00 

100.00 

98.00 

96.00 

94.00 

92.00 

90.00 

88.00 

86.00 


Gasoline 


$487.50 

416.00 

350.00 

300.00 

262.50 

240.00 

210.00 

182.50 

165.00 

152.00 

137.50 

122.00 

112.50 

107.50 

102.00 

98.00 

95.00 

92.50 

90.00 

87.50 

85.00 

82.50 

80.00 

78.00 

76.00 

74.00 

72.00 

70.00 


Attention  is  called  in  these  tables  to  the  high  allowance  for 
repairs  in  the  case  of  the  gasoline  and  gas  engine  and  the  high  coal 
consumption  assumed  for  the  steam  engine. 

Another  interesting  comparison  is  that  made  by  H.  A.  Clark 

*Unit  costs:  Coal,  $5  per  ton;  gas  $1.20  per  1000  cubic  feet,  at  760 
B.  T.  U. ;  gasoline,  $0.20  per  gallon. 


COST  OF  INSTALLATION  AND  OF  OPERATION      571 

in  a  paper  on  the  Diesel  Engine.*  In  this  case  the  computations 
are  carried  out  for  three  sizes  of  Diesel  engine,  Crossley  Gas 
Engine  and  Dowson  producer,  and  high-speed  compound  con- 
densing steam  engine.  The  conditions  assumed  are  partly  as 
follows,  the  remainder  being  given  in  the  table  itself. 

Cost  of  fuel  delivered : 

Diesel  engine,  crude  oil  at  $10.90  per  ton  =  appr.  3.8  c.  per 
gallon. 

Crossley  engine,  anthracite  at  $5.70  per  ton. 

Steam  engine,  coal  at  $3  per  ton. 
The  fuel  cost  is  based  on  the  following  assumption: 

For  the  Diesel,  the  consumption  has  been  taken  in  each  case 
as  the  mean  between  full  and  half-load  rates.  These  rates  were 
actually  determined  by  tests. 

For  the  Crossley,  1.5  to  1.25  pounds  of  coal  per  B.  H.  P.  hour 
plus  an  allowance  for  stand-by  losses. 

For  the  steam  engine,  4  to  3.5  pounds  of  coal  per  B.  H.  P.  hour 
for  the  lowest  and  highest  powers,  assuming  an  evaporation  of 
8  pounds  of  water  per  pound  of  coal. 

The  cost  figures  in  the  original  table  have  all  been  transposed 
to  dollars  and  cents.  The  computations  are  based  on  a  year  of 
2700  working  hours. 

In  the  discussion  on  Clark's  paper,  the  cost  computations 
were  rather  severely  criticised,  mainly  on  account  of  the  fuel 
costs  assumed.  The  claim  was  made  that  both  the  coal  consump- 
tion for  the  steam  engine  and  the  cost  of  the  steam  coal  was 
assumed  too  high,  and  that  the  cost  of  oil  at  3.8  c.  per  gallon  could 
only  apply  to  seaboard  towns.  As  far  as  American  conditions 
are  concerned,  the  assumption  regarding  the  steam  engine  would 
seem  to  be  about  right,  while  the  cost  of  anthracite  at  $5.70  per 
ton  for  the  gas  engine  is  certainly  not  too  low.  On  the  other 
hand,  the  price  of  3.8  c.  per  gallon  for  the  crude  oil  would  seem  to 
favor  the  Diesel  engine.  It  all  comes  to  the  point  that  applies 
to  all  computations  of  this  kind,  and  that  is  that  the  results  are 
strictly  applicable  only  to  the  locality  for  which  they  are  com- 
puted. Allowing  for  possible  difference  in  the  labor  costs,  how- 
ever, it  seems  to  the  writer  that  the  comparison  is  quite  fair  as 
between  the  steam  and  the 'gas  engine. 

*  Proc.  of  M.  E./ 1903,  II. 


572  ,   INTERNAL  COMBUSTION  ENGINES 

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COST  OF  INSTALLATION  AND  OF  OPERATION      573 

As  a  final  example  of  this  kind  of  hypothetical  computation, 
the  following  table  is  given.  The  figures  are  due  to  Mr.  L.  G. 
Findlay  of  the  De  La  Vergne  Machine  Company  of  New  York. 
They  were  presented  at  the  Dayton  meeting  of  the  Ohio  Society 
of  Mechanical,  Electrical,  and  Steam  Engineers,  and  were  pub- 
lished in  Power,  July,  1907.  The  table  is  very  complete  and  would 
repay  careful  study.  Especially  interesting  is  the  effect  of  the 
load  factor  on  operating  costs.  This  factor  is  here  defined  as 
the  average  load  on  the  plant  divided  by  the  rated  capacity  of  the 
plant. 

In  Clark's  tables  above  no  mention  is  made  of  the  load  factor 
and  it  is  evidently  assumed  to  be  100  per  cent.  That,  however, 
is  a  condition  existing  and  maintained  in  very  few  plants.  In 
fact,  if  it  were,  it  would  be  poor  engineering,  as  it  gives  the  plant 
but  very  little  overload  capacity.  The  marked  effect  that  a 
decrease  of  the  load  factor  from  100  per  cent  to  50  per  cent  has 
upon  operating  costs  is  very  clearly  brought  out  in  the  table. 
In  the  tables  given  below  for  actual  cost  data,  the  load  factor 
is  in  most  cases  even  lower  than  this. 

In  the  discussion  on  the  results  of  the  table  following  its 
presentation,  the  steam  men  objected  to  the  comparison  between 
the  steam  and  gas  plants  at  the  rated  load,  on  account  of  the 
much  greater  overload  capacity  of  the  steam  engine  plant.  Lines 
36,  37,  38,  and  39  of  the  table  are  computed  on  the  assumption 
that  80  per  cent  of  the  steam  used  by  the  engines  is  available  for 
heating,  but  no  standing  charges  are  made  against  the  heating 
plant. 

Turning  next  to  data  from  actual  practice,  the  first  of  the 
following  tables  was  given  by  Mr.  J.  E.  Dowson  in  a  paper  in  the 
Journal  of  the  Institute  of  Electrical  Engineers  April,  1904. 
The  table  refers  to  results  obtained  in  two  English  plants;  the  first 
is  equipped  with  Dowson  generators  and  Crossley  engines,  the 
second  with  the  same  type  of  producer  and  Westinghouse  vertical 
engines  of  comparatively  small  size.  In  spite  of  the  higher  cost 
of  coal,  the  greater  capacity  of  the  Walthamstow  plants  brings 
down  the  wage  and  repair  items  enough  to  make  the  total  works 
costs  not  far  different.  The  table  only  gives  works  cost,  and  it 
should  be  remembered  that  the  results  apply  to  English  condi- 
tions. 


574 


INTERNAL  COMBUSTION  ENGINES 


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COST  OF  INSTALLATION  AND  OF  OPERATION      575 


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576 


INTERNAL  COMBUSTION  ENGINES 


The  second  and  third  tables  following  are  due  to  Mr.  J.  R. 
Bibbins  of  the  Westinghouse  Machine  Company  and  were  pub- 
lished in  a  paper  on  the  Application  of  Gas  Power  to  Central 
Station  Work,  read  before  the  National  Electric  Light  Associa- 
tion at  Washington,  June,  1907.  Both  of  the  stations  mentioned 
use  natural  gas  for  fuel,  but  the  Bradford  plant  is  equipped  with 
rather  small  Westinghouse  vertical  engines,  while  the  Warren 
and  Jamestown  station  contains  two  large  direct  connected  units 
of  500  horse-power  each.  In  both  cases  the  load  factor  is  con- 
siderably less  than  50  per  cent;  in  the  case  of  the  Bradford  plant 
it  is  only  about  19  per  cent.'  The  figures  for  the  latter  plant  are 
remarkable  for  the  length  of  time  covered,  8J  years. 
WORKS  COST  OF  OPERATING  GAS  PLANTS 


PU 

int 

Midland  Railway  Co., 
Leicester 

Urban  District  Station, 
Walthamstow 

Engine: 
Capacity  tested  

300 

1500 

Number  

6 

7 

Make    

Length  of  run  
Load  factor  
K.  W.-hour  generated  
Remarks  —  service    .    . 

5  months 

200497 
Arc  and  incandescent 

12  months 
15.25 
659756 

Duty  of  plant:  * 
Los.  per  K.  W.-hour    . 
Lbs.  per  B.  H.  P.  . 

lighting,  Dowsongas. 

3 
2  25 

lighting,  Dowson  gas. 
-  2 

1     C 

Cost: 
Coal  per  ton    
Fuel  per  K.  W.-hour  
Oil,  waste,  water   . 
Wages    

$3.75 
.123c. 

.020c. 
oqop 

$6.50 
.17c. 

.095c. 

f)1  C~ 

Total  works  cost  power, 
cents  per  K.  W.-hour  .... 

Authority: 

.473c. 
R.  M.  DEELY, 

Supt.  Locomotives. 

.445c. 
F.  A.  WILKINSON, 

Elec.  Engineer  in  charge. 

WORKS  COST  OF  POWER  —  GAS  DRIVEN  CENTRAL  STATION 
BRADFORD  ELECTRIC  LIGHT  &  POWER  Co.,  BRADFORD,  PA. 

Station  capacity  (five  engines)    .  .  470  kilowatts 

.Number  of  years  in  operation 85 

Average  station  load  factor  ('03-'06) .''.....  '.'.  19^09  per  cent 

Average  gas  consumption  per  kilowatt-hour  ('03-'06)  25  5  cu.  ft. 

Average  heat  efficiency  at  switchboard 14.14  per  cent 

*  Including  "stand-by"  losses. 


COST  OF  INSTALLATION  AND  OF  OPERATION      577 


Works  Cost  of  Power 

Dollars  per  year. 
Average  8  years 

Cents  per  Kilowatt-hour. 
Average  4  years 

Fuel,  gas,  including  heating  
Station  wages 

$3,121 
3,068 

0.307 
0.410 

Oil,  waste  and  supplies 

454 

0.054 

Running  repairs  (total)     

848 

0.085 

Running  repairs  gas  engines  

285 

0.034 

Total  operating  cost    

$7,776 

0.890 

Engine  repairs  —  $0.36  per  horse-power  per  year. 
57.00  per  engine  per  year. 

.75  per  cent  on  investment. 
Fuel  —  Bradford  natural  gas. 

WORKS  COSTS  —  GAS  POWER  RAILWAY  PLANT 
WARREN  &  JAMESTOWN  STREET  RAILWAY  COMPANY 

Capacity  of  plant  (two  units)    600  kilowatts 

Average  time  operated  per  day 18.5  hours 

Average  output  per  day  4115  kilowatt  hours 

Average  load,  per  cent  rating    37  per  cent 


Works  Cost  of  Power 

Dollars  per  day 

Cents  per 
Kilowatt-hour 

Average  First  Four  Months,  1906: 
Fuel  gas  

$12.97 

0.315     ' 

Wages 

12  37 

0300 

Oil 

2.63 

0.064 

Repairs  and  miscellaneous  supplies  .  . 

3.29 

0.080 

Total 

$31.26 

0.759 

Fuel  —  "  Bradford  Sand  "  natural  gas. 

In  conclusion,  to  make  the  figures  in  the  above  tables  readily 
comparable  among  themselves,  the  cost  data  has  been  recom- 
puted to  the  basis  of  cost  in  cents  per  B.  H.  P.  hour  in  all  cases. 

Table  I  gives  the  total  operating  costs  for  small  and  medium 
sized  plants  as  computed  from  the  data  of  Webber  &  Clark. 
The  load  factor  is  in  all  cases  100  per  cent.  The  difference  in  the 
cost  of  steam  power  arrived  at  by  the  two  authorities  is  remark- 
able, Clark's  figures  being  less  than  50  per  cent  those  of  Webber. 
The  reason  for  this  is  found  in  two  directions,  different  assump- 
tions as  to  cost  of  coal,  $5.  per  ton  as  against  $3,  and  different 
assumptions  as  to  the  coal  consumption  per  horse-power.  Webber 


578 


INTERNAL  COMBUSTION  ENGINES 


assumes  as  high  as  20  pounds  of  coal  per  horse-power  for  a  6 
horse-power  plant,  and  charges  a  20  horse-power  plant  up  with  12 
pounds  per  horse-power-hour.  In  fact  Webber's  figures  are  very 
liberal  throughout  for  all  three  kinds  of  power. 

In  Table  II,  the  works  and  total  operating  costs  per  B.  H.  P.- 
hour  are  shown  side  by  side  as  computed  from  Findlay's  table. 

TABLE  I 

Total  Operating  Costs  per  B.  H.  P.-hour 
Small  and  Medium  Sized  Plants 


E 

Size  of  Plant 

o 

>, 

TCinH 

€ 

O  (-< 

•53 

Kind  of  Power 

of 

£ 

?D 

8 

10  |  16 

20 

24 

30 

35 

50 

80 

100 

100 

0 
J3 

Fuel 

2 

p 

I 

3 
< 

£ 

Cost  in  cents  per  B.  H.  P.-hour 

Steam  Engine  . 

Coal 

100 

3080 

13.9 

6.3 

5.1 

4.7 

4.5 

4.1 

4.0 

3.7 

3.1 

2.8 

Webber 

Gas  Engine    .  . 

111.  Gas 

100 

3080 

6.2 

4.6 

3.9 

3.6 

3.5 

3.3 

3.2 

3.1 

2.9 

2.8 

Webber 

Gas  Engine    .  . 

Gasoline 

100 

3080 

8.5 

4.9 

3.7 

3.3 

3.1 

2.8 

2.7 

2.6 

2.4 

2.3 

Webber 

Steam  Engine  . 

Coal 

100 

2700 

1.78 

1.26 

.98 

Clark 

Gas  Engine    .  . 

Prod.  Gas 

100 

2700 

1.38 

1.04 

.80 

Clark 

Oil  Engine, 

Diesel     .... 

Crude  Oil 

100 

2700 

1.08 

.78 

.64 

Clark 

TABLE  II 

Total  Operating  and  Works  Cost  per  B.  H.  P.-hour. 
Computed  from  Table  by  Mr.  L.  G.  Findlay. 
Works  costs  in  brackets. 


Kind  of  Power 

Hours  in 
Operation 
per  day 

Load 

Factor 

Size 
of  Plant 
B.  H.  P. 

Steam 

Bituminous 
Producer  Gas 

Anthracite 
Producer  Gas 

Cents  per  B.  H.  P.-hour 

24 

100 

'    1000 

.39  (    .30) 

.31  (.21) 

.39  (.30) 

24 

50 

1000 

.69  (  .41)' 

.54  (.33) 

.67  (.49) 

10.25 

100 

1000 

.53  (  .33) 

.46  (.22) 

.55  (.33) 

,  10.25 

50 

1000 

.88  (  .47) 

.84  (.36) 

.99  (.56) 

24 

100 

200 

.76  (  .69) 

.40  (.29) 

.43  (.38) 

24 

50 

200 

1.23  (1.10) 

.71  (.49) 

.86  (.66) 

10.25 

100 

200 

.88  (  .73) 

.59  (.33) 

.69  (.45) 

10.25 

50  . 

200 

.1.44  (1.15) 

1.11  (.59) 

1.26  (.78) 

COST  OF  INSTALLATION  AND  OF  OPERATION      579 


The  data  from  the  Bradford  and  Jamestown  plants  and  from 
the  two  English  plants  shows  the  following  results  for  the  works 
cost  per  B.  H.  P.-hour. 


Fuel 

Load 
Factor 

B.  H.  P. 

rated 

Works  Cost 
per  B.  H.  P.- 
hour  cents 

Plant 

Natural  gas  

19.09 

640 

.67 

Bradford 

Natural  gas  
Dowson  gas  
Dowson  gas  

37.0 
15.25 

800 
400 
2000 

.57 
.35 
.33 

Jamestown 
Midland  Railway 
Walthamstow 

From  these  figures,  and  those  of  Table  II,  the  conclusion 
seems  justified  that  it  should  be  easily  possible  to  produce  one 
brake  horse-power  in  a  fair  sized  plant,  say  not  under  200  horse- 
power, for  a  works  cost  of  from  .5  to  .75  cents  per  hour,  depend- 
ing upon  the  conditions  involved.  This  excludes  fixed  charges 
and  assumes  a  load  factor  in  the  neighborhood  of  50  per  cent. 


INDEX 


PAGE 

Abeille  carbureter 189 

Absolute  temperature 6 

Accumulators  or  storage  batter- 
ies    411 

Acetylene,  constants  for 211 

Adiabatic  and  isothermal 
changes,  graphical  ex- 
pressions for • .  .  ,  55 

Adiabatic  change    16 

expansion,  work    per- 
formed in 53 

line,  equation  of 52 

Admixture  of  benzol  to  alcohol      184 

After-burning 220 

Air  gas,  production  of    147 

Air  required   for  combustion  of 

alcohol    183 

Air  required  for  combustion.  .  .  .    136 

Air  thermometer 8 

Alcohol,  commercial,  table  of 
specific  gravities  and 

heating  values 183 

Alcohol,  air  required  for  com- 
bustion of 183 

Alcohol,  composition  and  heat- 
ing value  of  (  181 

Alcohol  engine     390 

vapor  air  mixtures   ....    203 

Alcohol,  denatured    183 

Alcohol  vaporizer,  Altman    ....    198 

Deutz    198 

Dresden    201 

Duerr    201 

S\viderski-Longuemarre   .  .  .    199 


PAGE 

Alcohol,  vaporizing  devices  for. .   196 

Allis-Chalmers  gas  engine    345 

Altman  alcohol  vaporizer    198 

American  Crossley  suction  pro- 
ducer      167 

Atomizing  or  spraying  carburet- 
ers      187 

Atomizer,  Hornsby-Akroyd  ....    193 

Attendance,  cost  of 565 

Automatic  cut-off  engine,  Jacob- 
son  271 

Automobile  engine,  Continental     373 

Franklin   372,374 

Moore    374 

Horch 373 

horse-power  rating  of 483 

Automobile  gasoline  engine  ....   372 

Auto-sparker 416 

Auxiliaries  and  piping,  cost  of.  .    548 
Auxiliary  spark  gap 409 


Barnett's  engine    236 

ignition  cock    392 

Barsanti  and  Matteucci  free  pis- 
ton engine    239 

Batteries,  primary  and  second- 
ary, method  of  connecting  420 

Beau  de  Rochas    243 

Beau  de  Rochas  or  Otto  cycle, 

theoretical    65 

Benzol 184 

admixture  of  to  alcohol   .  .  .    184 

Blast  furnace  gas,   composition 

and  heating  value  of  ....   209 


581 


582 


INDEX 


PAGE 

Blast  furnace  gas  engines,   fuel 

costs  for    561 

Blast  furnace  gas,  preparation  of  210 

value  of 560 

Bomb  calorimeter,  Mahler's    ...  129 

Brayton  cycle,  theoretical 69 

engine 248 

engine  diagram    250 

oil  engine,  test  of 250 

Brake  horse-power,  definition  of  38 

Brake,  Prony 39 

British  Thermal  Unit 14 

Brown,  engine  of 234 

Bruce-Merriam-Abbott  engine    .  275 
Buckeye  two-cycle  engine,  gov- 
erning of 467 

Buckeye  two-cycle  gas  engine  .  .  286 

Buffalo  tandem  engine 282 

Buildings  and  floor-space,  cost  of  549 


Calorie 14 

Calorific  intensity 144 

Calorimeter,  Carpenter's  coal    .  .    130 

Junker's  gas 131 

Mahler's  bomb 129 

Calorimetric  thermometers 11 

Campbell    oil-engine,     governor 

for 456 

Carbon,  heating  value  of 132 

Carbon  monoxide,  heating  value 

of 132 

Carbureter,  atomizing  or  spray- 
ing      187 

Carbureter,  bubbling,  type  of  .  .    185 

Daimler 188 

DeDion 190 

Gautier .....' 191 

Sintz 188 

surface      186 

Carbureters    185 

Carnot  cycle 62 

Carnot  or  reversible  engine 54 

Cells,  wet  and  dry 410 


PAGE 

Centrifugal  governors  for  hit-and- 
miss  regulation    454 

Charging  of  storage  batteries    .  .  414 

Classification  of  fuels 146 

heat  engines    .  .  17 
internal  combus- 
tion engines .  27 

Classification  of  producers 158 

Cleaning  of  blast  furnace  gas  for 

use  in  engines    210 

Clearances  and  compression  pres- 
sures   for    various    fuels, 

Otto  cycle,  table  of 90 

Clerk's  engine    255 

Clerk  engine  diagram 257 

engines,  tests  on 257 

Clerk's  experiments  on   specific 

heat 224 

Clerk-Lanchester  starter    432 

Closed  cycle,  definition  of 61 

Cockerill  engines 336 

Code  of  German  Society  of  En- 
gineers,   for    testing   gas 
producers  and  gas  engines ,  511 
Coefficient,  excess,  definition  of,  137 
Coefficient   of   fly-wheel    regula- 
tion   439 

Coefficient  of  governor  regulation  440 

Coke  oven  gas,  constants  for.  .  .  208 

Cold  gas  efficiency 151 

Cooling  water  conditions  affect- 
ing economy 530 

Combining  weights  and  volumes, 

for  gases 127 

Combination  gasoline  and  alco- 
hol vaporizer 202 

Combination  producers    173 

Combination  producer,  Crossley  173 

Deutz  double  zone    173 

Loomis-Pettibone 174 

Combination  systems  of  govern- 
ing   447 

Combustion,  air  required  for  ...  136 
Combustion  line,  Otto  cycle    ...  90 
Combustion   of   alcohol,    air   re- 
quired     183 


INDEX 


583 


PAGE 

Combustion,  pressure,  due  to    .  .   220 
products  of    136 

Comparative  cost  of  power  for 

various  prime  movers,  569-579 

Comparison   of   theoretical   and 

actual  heat  engines 61 

Comparison  of  various  theoret- 
ical cycles 73 

Composition   and    heating  value 

of  alcohol 181 

Composition  and    heating   value 

blast  furnace  gas 209 

Composition  and  heating  value 

of  gasoline    179 

Composition  and  heating  value 

of  kerosene 179 

Composition  of  oil  gas    207 

Composition  of  most  common 
commercial  gases,  graph- 
ical representation  214 

Composition  of  producer  gas  by 
volume  per  pound  of  car- 
bon gasified  152 

Composition  of  producer  gas  by 
weight  per  pound  of  car- 
bon gasified  151 

Compression,  effect  on  economy    532 

Compression  pressures  and  tem- 
peratures for  Otto  cycle, 
table  of 88 

Compression  pressures  and  clear- 
ances for  various  fuels, 
Otto  cycle,  table  of 90 

Compression  stroke,  Otto  cycle        86 

Compression,  temperature  due  to,  220   ' 

Condensers  in  spark  coils 404   , 

Conditions  required  for  the  prop- 
er formation  of  alcohol 
vapor-air  mixtures  203 

Constant  pressure  engines 30 

cycle 104 

Constant  pressure,     transfer     of 

heat  at     50 

Constant  temperature  engines    .    '31 

Constant    volume    or    explosion 

engines    28   | 


PAGE 

Constant    volume,     transfer    of 

heat  at    50 

Constants  for  acetylene 211 

coke  oven  gas  .  .  .   208 

Constants,  gas,  table  of 126 

Constants    for    gas  engine    fuel 

gases,  table  of   213 

Constants  for  illuminating  gas .  .   206 

natural  gas    212 

water-gas 212 

Conversion  of  solid  fuels  to  gas  146 
Coal  calorimeter,  Carpenter  ....    130 

Cost  of  attendance    565 

Cost  of  erection 548 

Cost    of   floor-space   and    build- 
ings    549 

Cost  of  fuel  for  illuminating  gas 

and  natural  gas  engines     558 
Cost  of  power  for  various  prime 

movers    569-579 

Cost  of  producers  and  engines    .   547 

oil  and  waste    564 

operation 533 

piping  and  auxiliaries  .  .   548 
Cost   of  water  for   cooling  and 

washing 561 

Costs,  fuel 553 

operating 568 

Crosby  indicator 34 

Crossley  combination  producer  .    173 

gas  engine 324 

Crossley  hit-and-miss  governor.   452 

vaporizer 194 

Grouse-Hinds  distributor 425 

double-ball  timer.   408 

Crude  oil 178 

Crude  oil  distillates 180 

Crude  oils,  table  of  heating  value 

and  composition    178 

Current,  sources  of 410 

Cycle,  Brayton,  theoretical   ....     69 

Carnot  .  .  : 62 

choice  of  best 79 

closed,  definition  of 61 

constant  pressure    104 

definition  of  .  3 


584 


INDEX 


PAGE 

Cycle,  Diesel,  theoretical 71 

Otto,  combustion  line 90 

Otto,  compression  stroke  . .     86 
Otto,  cyclic  efficiency  of  ...     68 

Otto,  exhaust  stroke    100 

Otto,  expansion  line 97 

Otto,  pressure  ratio  in     ...     92 

Cycle,  Otto,  requirements  for  best 

efficiency  in    100 

Cycle,  Otto,  suction  stroke    ....     84 

Cycle,  Otto,  table  of  allowable 
compression  pressures  and 
clearances  for  various  fuels  90 

Cycle,  Otto,  table  of  compres- 
sion pressures  and  tem- 
peratures    88 

Cycle,  Otto,  table  of  cyclic  effi- 
ciencies    69 

Cycle,  Otto,  table  of  volumetric 
efficiencies  and  suction 
pressures  86 

Cycle,  Otto,  typical  lower  loop 

diagrams 101 

Cycle,  Theoretical  Beau  de  Ro- 

chas  or  Otto 65 

Cycle,  two-stroke    .  . 102 

Cycles,  theoretical,  comparison  .      73 

Cyclic  efficiency,  definition  of .  .      62 

Cyclic    efficiency    of    theoretical 

Otto  cycle 68 

Cyclic  efficiencies  for  Otto  cycle, 

table  of  .  69 


D 

Daimler  carbureter 188 

Dashboard  spark  coil 406 

DeDion  carbureter 190 

Delamar  hit-and-miss  governor.   454 
De  La  Vergne  two-cycle  oil  en- 
gine     380 

Denatured  alcohol 183 

Denaturizing  agents  for  alcohol, 

table  of 184 

Depreciation  of  plant  and  build- 
ings    553 


PAGE 

Design,  general  features  of    ....   263 
Determination   of  excess  coeffi- 
cient  from   exhaust  gas- 
analyses    143 

Deutz  alcohol  vaporizer 198 

Deutz  double-zone  combination 

producer     173 

Deutz  gas  engine 351 

pressure  producer    162 

suction  producer 165 

Development  of  the  Diesel  en- 
gine     259 

Development  of  the  gas  engine 

industry    258 

Diagram,  Clerk  engine   257 

Diagram,      entropy,     graphical 

construction  of    120 

Diagram,  entropy,  interpretation 

of 119 

Diagram,  entropy,  mathematical 

construction  of    112 

Diagram  of  Lenoir  engine 242 

Diagram    pressure    volume,    de- 
fined             3 

Diagrams,  Diesel  engine 106 

indicator,  forms  of    40 

lower  loop,  Otto  cycle 101 

Otto  cycle 94 

Diesel  cycle,  theoretical 71 

engine 385 

Diesel  engine  diagrams 106 

Diesel  engine,  development  of    .    259 

governor  for 459 

Diesel  engines,  early,  tests  on.  .   262 

Dissociation,  theory  of 98 

Distributor,  Grouse-Hinds 425 

high  tension 423 

Leavitt 426 

Dresden  alcohol  vaporizer 201 

Diirr  alcohol  vaporizer 201 

Dynamos  and  magnetos 415 


E 


Economist  crude  oil  vaporizer    .    195 


INDEX 


585 


PAGE 

Efficiency,  cyclic,  definition  of .  .  62 
Efficiency,  cyclic,  of  theoretical 

Otto  cycle 68 

Efficiency,  hot  gas    151 

cold  gas 151 

Efficiencies  for  Otto  cycle,  table  of  69 
Ehrhardt    and    Sehmer    engine, 

governor  for 461 

Ejector  muffler    428 

Electrical  thermometers 8 

starters 436 

Energy,  kinetic 2 

Engine,  Barnett    236 

Brayton    248 

Brayton  oil,  test  of 250 

Brown 234 

Carnot  or  reversible    54 

Cayley's    26 

Clerk 255 

Clerk,  tests  on 257 

Engine  diagram,  Clerk 257 

Brayton    250 

Engine  diagrams,  Diesel    106 

Engine,  Diesel,  development  of  259 

furnace  gas 25 

Engine,    free   piston,    Otto   and 

Langen 244 

Engine,   gas,   method   of  opera- 
tion   26 

Engines,  gunpowder 233 

Engine,  Hugon    242 

Engine  indicator 32 

Engine,  Lebon 234 

Lenoir 239 

Lenoir,  diagram  of    242 

Engine,    Lenoir,    gas    consump- 
tion of 242 

Engine,  Otto    251 

Engines,  Otto,  tests  on 254 

Engine,  Papin 232 

Perry 238 

Robert  Street 233 

Stirling  hot-air 24 

Wright    :..  235 

Engine  economy  as  affected  by 

compression 532 


PAGE 

Engine  economy,  as  affected  by 

cooling  water  conditions  530 

Engine  economy  as  affected  by 

piston  speed  .          530 

Engine  economy  as  affected  by 
variation  in  fuel  mix- 
ture    533 

Engine  economy  depending  upon 

load 537 

Engine  economy  depending  upon 

point  of  ignition    534 

Engines,  constant  pressure    ....     30 
constant  temperature 31 

Engines,  constant  volume  or  ex- 
plosion    28 

Engines,  Diesel,  tests  on    262 

heat,  classification  of    17 

Engines,    heat,    comparison    of 

theoretical  and  actual    .  .     61 

Engines,  hot-air 22 

Engines,    internal    combustion, 

classification  of    27 

Entropy    15,  107 

Entropy  diagram,  graphical  con- 
struction of  120 

Entropy  diagram,  interpretation 

of 119 

Entropy  diagram,  mathematical 

construction  of    112 

Entropy  relations,  general     ....    109 

Erection,  cost,  of 548 

Ericsson  hot-air  engine    22 

Excess  coefficient,  definition  of  .    137 

Excess  coefficient  from  exhaust 

analysis 143 

Expansion  line,  Otto  cycle 97 

Experiments  on  specific  heat  by 

Clerk 224 

Experiments  on  specific  heat  by 

Langen 220 

Experiments  on  specific  heat  by 

Mallard   and   LeChatelier  220 

Exhaust  gas  analysis,  excess  co- 
efficient from  143 

Exhaust  gas,  computations  on  .    138 
stroke,  Otto  cycle 100 


586 


INDEX 


PAGE 

Explosibility    of    fuel    mix- 
tures    215,218 

Explosion    or   constant    volume 

engines   28 

Explosion  recorder,  Mathot  ....   500 

Explosion,  time  of    227 

Explosive  mixture    215 


Fairbanks  engine 288 

Fairbanks,  Morse  &  Co.,  engine.   277 
Fairbanks-Morse  crude  oil  vapor- 
izer    389 

Fairbanks-Morse     suction     pro- 
ducer      168 

Fay  and  Bowen  make-and -break 

igniter 400 

Felten  and   Guilleaume  electric 

starter     436 

Fixation  of  tar-forming  gases  in 

producer  gas    157 

Flame  propagation,  velocity  of  .   227 
Floor-space  and  buildings,  cost 

of 549 

Fly-wheel  regulation,  coefficient 

of 439 

Fly-wheel  weights,  table  of  ....    440 

Foos  gasoline  engine 358 

Forms  of  indicator  diagrams  ...      40 
Formula  for  mean  effective  pres- 
sure, Grover's    472 

Four-cycle  gas  engine,  Koerting .   280 
Four-cycle  gasoline  engine,  Stre- 

linger 362 

Four-terminal  spark  coil    405 

Franklin  automobile  engine,  372,  374 
Free-piston  engine,  Barsanti  and 

Matteucci 239 

Free-piston    engine,    Otto    and 

Langen 244 

Fuel  costs 553 

Fuel  costs  for  blast  furnace  gas 

engines    561 

Fuel  costs  for  gasoline  engines.  .   561 


PAGE 
Fuel  costs  for  illuminating  gas 

and  natural  gas  engines .  .   558 
Fuel  costs  for  producer  gas  en- 
gines       559 

Fuel  costs  for  steam  engines  .  .  .   557 
steam  turbines    .  .   558 

Fuel  gases,  constants  for 213 

Fuel  mixture,  computations  on.    138 
Fuel  mixture,   variation  in,  af- 
fecting economy    533 

Fuel  mixtures,  explosibility  of .  .   215 

Fuels,  classification  of    146 

liquid,  heating  value  of    ...    134 
solid,  heating  value  of    ....    135 

Furnace  gas  engine 25 

Fusion  thermometers  .  11 


Gas   and    oil    engines,    tests   of, 

Code  of  A.S.M.E 487 

Gas  calorimeter,  Junker's    131 

Gas,  coke  oven,  constants  for  .  .   208 
Gas    constants    R    for    perfect 

gases,  table  of    48 

Gas  constants,  table  of 126 

Gas  consumption  of  Lenoir  en- 
gine      242 

Gas,  blast  furnace,  composition 

and  heating  value  of  ....   209 
Gas,  illuminating,  constants  for,  206 

natural,  constants  for 212 

oil,  composition  of    207 

oil,  heating  value  of 208 

perfect,  specific  heat  of    ...      12 
Gas  producers  and  engines,  tests 

of 542 

Gas  producers  in  practice    156 

Gas,  waver,  constants  for 212 

Gases,    combining   weights    and 

volumes    127 

Gases,   commercial,  composition 

of 214 

Gases,  fuel,  constants  for 213 

Gases,     illumination,     table     of 

composition 207 


INDEX 


587 


PAGE 

Gases,  perfect,  characteristics  of.  45 

Gases,  perfect,  laws  of 40 

Gases,  perfect,  .table  of  specific 

volumes 47 

Gases,  specific  heat  of    48 

Gas  engine,  Allis-Chalmers    ....  345 

Bruce-Merriam-Abbott  ....  275 

Buckeye  two-cycle    286 

Buffalo  tandem   282 

Crossley    324 

Deutz    351 

Diesel    385 

Fairbanks,    288 

Fairbanks,  Morse  &  Co.  .  .  .  277 

furnace 25 

Hautefeuille 232 

Gas  engines,  Jacobson    267 

Gas   engine,    Koerting    four- 
cycle    280 

Koerting  two-cycle 313 

Nurnberg    339 

Gas  engine,  Niirnberg,  table  of 

standard  sizes    346 

Gas  engine,  Oechelhauser    355 

Olds    292 

Philadelphia  Otto   291 

Premier 347 

Riverside    320 

Sargent 310 

Gas  engines,  Snow 329 

Gas  engine,  Tod    306 

Warren  hit-and-miss 295 

Westinghouse 266 

Westinghouse  horizontal.  .  .  304 
Gas  engine,  Westinghouse  verti- 
cal single-acting  tandem,  306 

Gas  engine  governing 439 

Gas    engine    industry,    develop- 
ment of 258 

Gas  engine  regulation 439 

tests,  tables  of  .  .544,  545 
Gas  engines  and  producers,  cost 

of 547 

Gas  engines  and  gas  producers, 

results  of  tests 542 

Gas  engines,  Cockerill 336 


PAGE 

Gas  engines,  blast  furnace,  fuel 

costs  for    561 

Gas   engines,    illuminating    and 

natural,  fuel  costs  for .  . .   558 
Gas   engines,  method    of   opera- 
tion       26 

Gas  engines,  methods  of  testing    486 
producer,  fuel  costs  for    .  .  .   559 
small  and.  medium  size  ....  '265 
Gasification  in  pressure  produc- 
ers, rate  of 177 

Gasoline,  composition  and  heat- 
ing value  of   179 

Gasoline,  mixing  devices  for  ...    185 
Gasoline  engine,  automobile ....   372 

Foos 358 

Lozier  two-cycle    364 

Olds 360 

Standard  marine 367 

Strelinger  four-cycle 362 

Gasoline  engines    358 

fuel  costs  for    561 

marine 361 

Gautier  carbureter    191 

Generators,   current,  mechanical 

forms  of 415 

German    Society    of    Engineers, 
Code  for  testing  gas  pro- 
ducers  and    gas    engines  511 
Gibbon  kerosene  vaporizer    ....    193 
Governor,  Campbell  oil  engine .  .   456 

Crossley  hit-and-miss 452 

Delamare  hit-and-miss  ....    454 

Diesel  engine 459 

Governor,  Ehrhardt  and  Sehmer 

engine   461 

Gov^nor,   Hornsby-Akroyd  en- 
gine    458 

Governor,    Koerting    four-cycle 

engine   460 

Governor,  Nurnberg  engine  ....   458 
Governor  regulation,  coefficient  of  440 

Governor,  Robey 455 

Springfield  hit-and-miss  .  .  .   453 
.Governor,  Westinghouse  vertical 

engine   .  .    460 


588 


INDEX 


PAGE 

Governing    Buckeye    two-cycle 

engine 467 

Governing  of  gas  engines 439 

Governing,  hit-and-miss  system    444 

Governing  of  Koerting  engine  .  .    468 

Governing  of  Oechelhauser  en- 
gine    467 

Governing  of  two-cycle  engines     449 

Governing,  Letombe  system  of  .    465 
Reinhardt's  method.  ......    464 

Reichenbach  engine    463 

Governing  small  two-cycle  en- 
gine    467 

Governing  systems 441 

Governing  by  varying   time   of 

ignition 449 

Governing  by  varying  the  qual- 
ity of  the  fuel  mixture .  .  444 

Governing  by  varying  the  quan- 
tity of  fuel  mixture 446 

Governors,  pendulum,  for  hit- 
and-miss  regulation  ....  450 

Governors,  centrifugal,  for  hit- 
and-miss  regulation  ....  454 

Governors,  mechanical  details  of,  450 

Graphical    construction    of    the 

entropy  diagram  .  ......    120 

Graphical  expressions  for  adia- 
batic  and  isothermal 
changes  .  . 55 

Graphical  representation  of  com- 
position of  most  common 
commercial  gases 214 

Grover's  formula  for  mean  effect- 
ive pressure  472 

Giildner's  method  of  determin- 
ing horse-power 477 

Gunpowder  engines 233 

H 

Hammer  break  ignition 398 

Hautefeuille,  Abbe,  gas  engine  of  232 

Hay  vaporizer 190 

Heat  at  constant  pressure,  trans- 
fer of  .  50 


PAGE 

Heat  at  constant  volume,  trans- 
fer of 50 

Heat  balance   539 

Heat,  definition  of    3 

Heat  engines,  classification  of .  .      17 
Heat    engines,    theoretical    and 

actual,  comparison  of    .  .     61 
Heat,  mechanical  equivalent  of       15 

relation  of  to  entropy 54 

Heat  unit 14 

Heating  value  and  composition 
for  true  explosive  mix- 
tures from  liquid  fuels, 

table  of 217 

Heating  value  and  composition 

of  alcohol 181 

Heating  value  and  composition 

of  blast  furnace  gas    ....    209 
Heating  value,  definition  of    ...    129 

Heating  value  of  carbon    132 

Heating  value  of  carbon  mon- 
oxide    132 

Heating  value  of  crude  oils,  table 

of 178 

Heating  value  of  gasoline    179 

hydrogen   ....    132 

kerosene 179 

liquid  fuels    .  .    134 

oil  gas 208 

solid  fuels    ...    135 
Heating  values  and  specific  grav- 
ities of   commercial  alco- 
hol, table  of 183 

Heating  values  of  hydrocarbons, 

table  of * .    132 

Heating  values  of  true  explosive 

mixtures,  table  of 216 

High  tension  distributor    423 

jump-spark  system  423 
Hit-and-miss  engine,  Jacobson .  .   268 

Warren 295 

Hit-and-miss  governor,  Crossley  452 

Delamare 454 

Springfield    453 

Hit-and-miss  system  of  govern- 
ing   , 442 


INDEX 


589 


PAGE 

Horch  automobile  engines 373 

Horizontal  gas  engine,  Westing- 
house  304 

Horsnby-Akroyd  atomizer 193 

Horrisby-Akroyd     engine,     gov- 
ernor for 458 

Hornsby-Akroyd  oil  engine  ....   376 
Horse-power,  brake,  definition  of     38 

Horse-power  defined 1 

Horse-power,  determination  from 

mean  effective  pressure.  .    472 
Horse-power  from  standard  air 

reference  diagram   476 

Horse-power,  Giildner's  method    477 
Horse-power,    indicated,    defini- 
tion of 38 

Horse-power  rating  of  automo- 
bile engines    483 

Hot-air  engine,  Ericsson    22 

Stirling 24 

Hot-air-engines 22 

Hot  gas  efficiency   1.51 

Hot  tube  igniter,  Koerting    ....   395 

Newton's    238 

Hot  tube  ignition    394 

with  timing  valve  ....    395 

Hugon  engine    242 

Hydrocarbons,  table  of  heating 

values  of 132 

Hydrogen,     lower     and     higher 

heating  value  of    132 

Hyperbola,  methods  of  drawing      43 


Ignition 392 

Ignition  by  electric  spark    397 

heat  of  compression  396 

hot  tube 394 

open  flame 392 

Ignition  cock,  Harriett's 392 

Ignition,  hammer  break 398 

jump-spark 401 

make-and-break    ....:....  397 
Ignition,   variation  in,  affecting 

economy 534 


PAGE 

Igniter,  Fay  and   Bowen  make- 
and-break  400 

Igniter,  hot  tube,  Newton's  ....   238 

Koerting,  hot  tube. 395 

Koerting  open  flame 393 

Illuminating  gas,  constants  for.   206 
Illuminating  gases,  table  of  com- 
position of    207 

Index  for  expansion  and  com- 
pression lines,  method  of 

finding 115 

Indicated    horse-power,     defini- 
tion of 38 

Indicators,  engine 32 

Indicator,  Crosby    •  •  • .-      34 

optical 35 

Tabor    34 

Thompson    33 

Indicator  diagrams,  forms  of .  .  .     40 
Inertia    governors    for    hit-and- 
miss  regulation    450 

Internal     combustion     engines, 

classification  of    27 

Isothermal  line,  equation  of.  ...     52 
Isothermal    and    adiabatic 
changes,      graphical     ex- 
pressions for 55 

Isothermal  change    16 

Isothermal  expansion,  work  per- 
formed in    .  53 


Jacobson  automatic    cut-off   en- 
gine      271 

Jacobson  gas  engines    267 

hit-and-miss  engine .  .  .   268 
throttling  engine    ....   272 

Jump-spark  ignition 401 

Jump-spark  and  make-and-break 

systems  compared 410 

Jump-spark    system,   high    ten- 
sion    423 

Junker's  gas  calorimeter    131 


590 


INDEX 


K 

PAGE 

Kerosene,  composition  and  heat- 
ing value  of    179 

Kerosene  vaporizer,  Gibbon    .  .  .  193 

Kinetic  energy 2 

Koerting  engine,  governing  of    .  468 

four-cycle  gas  engine  .  280 

Koerting  four-cycle  engine,  gov- 
ernor for 460 

Koerting  hot  tube  igniter    395 

open  flame  igniter    .  .  .  393 

suction  producer 166 

pressure  producer  ....  161 

Koerting    suction    producer    for 

peat 172 

Koerting  two-cycle  engine 313 


Lacoste  timer 407 

Langen's  experiments  on  specific 

heat 220 

Laws  of  perfect  gases  .  . 46 

Leavitt  distributor 426 

Lencauchez  double-zone  suction 

producer 170 

Lencauchez  suction  producer    .  .  170 

Lenoir  engine 239 

•  diagram  of 242 

gas  consumption  of 242 

Letombe  system  of  governing.  .  465 

Lebon's  engine  .  . 234 

Limits  of  explosibility  for  fuel 
mixtures  made  from  dif- 
ferent fuels  218 

Limit  of  piston  speed 471 

Liquid  fuel  engines 358 

Liquid  fuels,  heating  value  of .  .  .  134 

Liquid  fuels,  mixing  devices  for.  185 
Loomis-Pettibone     combination 

producer 174 

Lowe  system  for  making  oil  gas.  196 

Low  tension  system  of  wiring.  .  421 
Lower  and  higher  heating  value 

of  hydrogen 132 


PAGE 

Lower  loop  diagrams,  Otto  cycle  101 
Lozier  two-cycle  marine  gasoline 

engine   364 

Lunkenheimer  mixing  valves   . .   187 

M 

Magneto,  action  of    416 

Magnetos  and  dynamos 415 

Magnetos,  systems  of  wiring  em- 
ploying    422 

Mahler's  bomb  calorimeter  ....    129 

Maintenance  and  repairs 567 

Make-and -break  and  jump-spark 

systems  compared 410 

Make-and-break  ignition 397 

Mallard    and    LeChatelier's    ex- 
periments on  specific  heat  220 

Manograph 35 

Marine   gasoline   engine,    Lozier 

two-cycle    364 

Marine  gasoline  engine,  Standard  367 

Marine  gasoline  engines 361 

Mathematical  construction  of  the 

entropy  diagram 112 

Mathot  explosion  recorder 500 

Matteucci  and  Barsanti  free  pis- 
ton engine    239 

Mean  effective  pressure,  Grover's 

formula 472 

Mean   effective   pressure,    tables 

for  determining 473 

Mechanical  details  of  governors     450 
equivalent  of  heat    .      15 
forms   of  generators  415 
Method   of   connecting    up    pri- 
mary and  secondary  bat- 
teries      ^120 

Method  of  drawing  hyperbola  .  .      43 
Method  of  finding  index  for  ex- 
pansion arid  compression 

lines 115 

Method     of     governing,     Rein- 

hardt's    464 

Method    of    operating    gas    en- 
gines      20 


INDEX 


591 


PAGE 

Method  of  test,  Code  of  1901, 

brake  horse-power 497 

Methods  of  test,  Code  of  1901, 
calibration  of  instru- 
ments   488 

Methods  of  test,  Code  of  1901, 
computation  of  temper- 
atures    503 

Methods  of  test,  Code  of   1901, 

duration  of  tests 492 

Methods  of  test,  Code  of  1901, 

heat  balance   502 

Methods  of  test,  Code  of  1901, 

heat  units  consumed   .  .  .   493 

Methods  of  test,  Code  of  1901, 

indicated  horse-power.  .  ..  494 

Methods  of  test,  Code  of  1901, 

indicator  diagrams 501 

Methods  of  test,  Code  of  1901, 

measurement  of  fuel  ....   493 

Methods  of  test,  Code  of  1901, 
measurement  of  jacket 
water , 494 

Methods  of  test,  Code  of  1901, 

speed  determination  ....   498 

Methods  of  test,  Code  of  1901, 

standards  of  economy.  .  .   501 

Methods  of  test,  Code  of  1901, 
starting  and  stopping 
tests 493 

Mietz  and  Weiss  oil  engine 383 

Mixing  devices  for  gasoline    ....    185 
liquid  fuels    .    185 

Mixing  valves,  Lunkenheimer  .  .    187 

Mond  pressure  producer 163 

Mond  process  for  making  pro- 
ducer gas  163 

Moore  automobile  engine 374 

Morgan  pressure  producer 160 

Muffler,  ejector    428 

Powell 428 

Mufflers  .  ,  .426 


X 


Natural  gas,  constants  for 212 


PAGE 

Newton's  hot  tube  igniter 238 

Non-trembler  spark  coil 402 

Nurnberg  engine 339 

governor  for 458 

Nurnberg  gas  engine,     table     of 

standard  sizes 346 


O 


Oechelhauser  engine,  governing 

of 467 

Oechelhauser  gas  engine    355 

Oil   and   gas  engines,   tests,   of, 

Code  of  A.S.M.E. 488 

Oil  and  waste,  costs  of 564 

Oil,  crude,  distillates    180 

crude 178 

Oils,    crude,    table    of    heating 

value  and  composition  .  .  178 

Oil  engine,  Brayton,  test  of.  ...  250 

De  La  Vergne  two-cycle  ...  380 

Hornsby-Akroyd 376 

Mietz  and  Weiss    383 

Priestman 388 

Oil  engines 375 

Oil  gas,  composition  of 207 

heating  value  of    208 

Lowe  system  for  making   .  .  196 

Olds  gas  engine   292 

Olds  gasoline  engine 360 

Open  flame  igniter,  Koerting    .  .  393 

ignition    392 

Operating  costs 568 

Operation,  cost  of 533 

Optical  indicator 35 

pyrometers 9 

Otto  or  Beau  de  Rochas  cycle, 

theoretical    65 

Otto  cycle,  combustion  line    ...  90 

compression  stroke 86 

diagrams,  typical 94 

exhaust  stroke 100 

expansion  line    97 

pressure  ratio  in 92 


592 


INDEX 


PAGE 

Otto  cycle,  requirements  for  best 

efficiency  in    100 

Otto  cycle,  suction  stroke 84 

Otto  cycle,  table  of  allowable 
compression  pressures 
and  clearances  for  various 
fuels 90 

Otto  cycle,  table  of  compression 
pressures  and  tempera- 
tures    88 

Otto  cycle,  table  of  cyclic  effi- 
ciencies    69 

Otto  cycle,  table  of  volumetric 
efficiencies  and  suction 
pressures 86 

Otto    cycle,    theoretical,    cyclic 

efficiency  of    68 

Otto  cycle,  two-stroke 102 

Otto   cycle,    typical   lower   loop 

diagrams 101 

Otto  engine    251 

engines,  early,  tests  on ....   254 

Otto  and  Langen  free  piston  en- 
gine    244 

Otto-Langen  free  piston  engine, 

table  of  tests    :  .  .  .   247 

Otto-Langen  free  piston  engine, 

typical  diagram 248 

Otto  gas  engine,  Philadelphia  .  .   291 


Papin's  engine 232 

Pendulum  or  inertia  governors 
for  hit-and-miss  regula- 
tion    450 

Perfect  gases,  characteristics  of     45 

laws  of    .  .  .  .• 46 

Perfect  gas,  specific  heat  of  ....      12 
Perfect  gases,   table   of   specific 

volumes 47 

Perry's  engine 238 

Petreano  surface  carbureter.  .  .  .    187 

Philadelphia  Otto  engine 291 

Piping  and  auxiliaries,  cost  of    .    54 S 


PAGE 

Piston  speed,  effect  on  economy,  530 

limit  of 471 

Pittsfield  timer    '407 

Poetter  pressure  producer  162 

Powell  muffler 428 

Power  of  gas  engines   471 

Premier  gas  engine 347 

Pressure  after  combustion 220 

producers 159 

producer  capacities  ...    176 
Pressure  producers,  rate  of  gasi- 
fication     177 

Pressure  producer,  Deutz    162 

Koerting 161 

Mond 163 

Morgan 160 

Poetter 162 

Taylor 159 

Wile 160 

Pressure  ratio  in  the  Otto  cycle       92 
volume  diagram  defined       3 

Priestman  oil  engine 388 

vaporizer 194 

Prime  movers,  comparative  cost 

of  power  for 569-579 

Producers  and  gas  engines,  cost 

of 547 

Producers,  classification  of    ....    158 

combination 173 

Producer,  combination,  Crossley    173 
Producer,     combination,     Deutz 

double-zone    173 

Producer,  combination,  Loomis- 

Pettibone 174 

Producer  details 175 

gas    : 149 

Producer  gas,  composition  of  by 
volume  per  pound  of  car- 
bon gasified  152 

Producer  gas,  determination  of 
weight  and  volume  per 

pound  of  carbon    151 

Producer  gas  engines,  fuel  costs 

for 559 

Producer  gas,  fixation  of .......    157 

gas,  Mond  process    ...    163 


593 


PAGE 

Producer  plants,  tests  of     546 

Producers,  pressure 159 

Producer,  pressure,  Deutz 162 

Koerting 161 

Mond    163 

Morgan 160 

Poetter 162 

Taylor 159 

Wile 160 

Producers,  suction    165 

Producer,      suction,     American 

Crossley    167 

Producer,  suction,  Deutz 165 

Fairbanks-Morse 168 

Koerting .  166 

Koerting  for  peat    172 

Lencauchez    170 

Riche 169 

Producer  yield,  theoretical    ....  153 

Production  of  air  gas 147 

water  gas 147 

Products  of  combustion 136 

Prony  brake 39 

Pyrometers 7 

optical 9 


Quality  governing 444 

Quantity  governing    446 


R 


Rate  of  gasification  in  pressure 

producers 177 

Rate  of  work   1 

Rating  of  storage  batteries 413 

Regulation,    coefficient    of    fly- 
wheel  439 

Regulation,  governor 440 

Regulation  of  gas  engines   439 

Reichenbach    engine,    governing 

of 463 

Reinhardt's  method  of  governing  464 
Relation  of  heat  to  entropy    ...     54 


PAGE 

Repairs  and  maintenance    567 

Requirements  for  best  efficiency 

in  Otto  cycle    100 

Requirements  for  proper  scav- 
enging of  cylinder,  two- 
cycle  engine 103 

Reversible  engine,  Carnot 54 

Riche  suction  producer    169 

Riverside  gas  engine 320 

Robey  governor 455 


S 


Sargent  gas  engine   310 

Scavenging  of  cylinder,  two- 
cycle  engine,  require- 
ments for  103 

Second  law  of  thermodynamics       55 

Sintz  carbureter    188 

timer 406 

Snow  gas  engines    329 

Solid  fuels,  heating  value  of.  ...    135 

Sources  of  current 410 

Spark  coil,  action  of 402 

dashboard 406 

four-terminal   405 

three-terminal 405 

Non-trembler 402 

trembler 403 

Spark  gap,  auxiliary    409 

coils,  condensers  in' 404 

•  coils,  types  of 405 

plugs    4C6 

Specific  gravities  and  heating 
values  of  commercial  al- 
cohol, table  of 183 

Specific  heat  at  constant  pres- 
sure    13 

Specific  heat  at  constant  volume     13 
Specific    heat    experiments    by 

Clerk 224 

Specific    heat    experiments    by 

L:in«en 220 

Specific    heat    experiments    by 

Mallard  and  LeChatelier.   220 


594 


INDEX 


PAGE 

Specific  heat,  definition  of 12 

Specific  heat  of  perfect  gas  ....  12,  48 
Specific     heat     variation     with 

temperature 220 

Specific  heats,  table  of 13 

Specific  volumes  of  perfect  gases, 

table  of 47 

Spraying  or  atomizing  carburet- 
ers     187 

Springfield    hit-and-miss    gover- 
nor    453 

Standard  marine  gasoline  engine  367 

Starter,  Clerk-Lanchester    432 

Felten  arid  Guilleaume  ....  436 

Starting  apparatus 428 

Starting  by  auxiliary  source  of 

power    431 

Starting  by  compressed  air     .  .  .  433 

electricity 436 

fuel  mixture 431 

means  of  crank  ....  429 

Steam  engines,  fuel  costs  for  .  .  .  .557 

turbines,  fuel  costs  for  .  .  558 

Stirling  hot-air  engine    24 

Storage    batteries    or    accumu- 
lators    411 

Storage  batteries,  charging  of .  .  414 

rating  of 413 

testing  of    414 

Stratification,  theory  of  .......  97 

Strelinger  four-cycle  gasoline  en- 
gine    362 

Street,  Robert,  engine  of 233 

Suction  plants,  volume  of  scrub- 
ber    176 

Suction  pressures  and  volumetric 
efficiencies  for  Otto  cycle, 

table  of 86 

Suction  producers 165 

Suction      producer,      American 

Crossley    167 

Suction  producer,  Deutz    165 

Fairbanks-Morse 168 

Lencauchez 170 

Suction    producer,    Lencauchez, 

double-zone   .  .170 


PAGE 
Suction  producer,  Koerting  ....    166 

Koerting,  for  peat 172 

Riche 169 

Suction  stroke  of  Otto  cycle  ...     84 

Surface  carbureter 186 

Swiderski-Longuemarre    alcohol 

vaporizer    199 

System  of  governing,  Letombe.   465 
System     of     wiring     employing 

magnetos    422 

System  of  wiring,  low  tension.  .   421 

Systems  of  governing 441 

combination 447 

System    of   governing,    hit-and- 
miss 442 

Systems  of  wiring   420 


Tables  for  determining  mean 

effective  pressure  473 

Table  of  allowable  compression 
pressures  and  clearances 
for  various  fuels,  Otto 
cycle  90 

Table  of  combining  weights  and 

volumes  for  gases  128 

Table  of  composition  and  heating 
value  for  true  explosive 
mixtures  from  liquid  fuels  217 

Table  of  composition  of  typical 

illuminating  gases 207 

Table  of  compression  pressures 
and  temperatures  for 
Otto  cycle 88 

Table  of  constants  for  gas-engine 

fuel  gases  213 

Table  of  cyclic  efficiencies  for 

Otto  cycle  69 

Table  of  denaturizing  agents  for 

alcohol  184 

Table  of  engine  tests    544,  545 

Table  of  gas  constants  R  for  per- 
fect gases  48 

Table  of  heating  value  and  com- 
position of  crude  oils.  ...  178 


INDEX 


595 


PAGE 

Table  oT  heating  values  of  hydro- 
carbons    132 

Table  of  heating  values  of  true 

explosive  mixtures    216 

Table     of    relative     fly-wheel 

weights 440 

Table  of  specific  gravities  and 
heating  values  of  com- 
mercial alcohol  183 

Table  of  specific  heats    13 

Table  of  specific  heats  for  per- 
fect gases  48 

Table  of  specific  volumes  of  per- 
fect gases  47 

Table   of  standard   sizes   Niirn- 

berg  gas  engine '  346 

Table  of  tests  on  producer  plants,  546 
thermometric  scales    .  .        5 
Table    of    true    explosive    mix- 
tures,   for    commercial 

gases 216 

Table  of  vapor  tension  for  alco- 
hol and  water  204 

Table  of  various  gas  constants.  .    126 
Table  of  volumetric  efficiencies 
and  suction  pressures  for 

Otto  cycle 86 

Tabor  indicator 34 

Tandem  .gas  engine,  Buffalo    .  .  .    282 

Westinghouse 306 

Tar-forming  gases,  fixation  of.  .    157 

Taylor  pressure  producer 159 

Temperature,    absolute 6 

Temperature  after  combustion  .    220 

Temperature,  definition  of 3 

Temperatures  and  compression 
pressures  for  Otto  cycle, 

table  of 88 

Temperature  scales 5 

Test  on  Brayton  oil  engine 250 

Tests  of  Clerk  engines    257 

Tests  of  engines  and  gas  produc- 
ers, results  of 542 

Tests  of  gas  engines    544,  545 

on  early  Diesel  engines    .  .    262 
on  early  Otto  engines  ....   254 


PAGE 
Tests  of  gas  and  oil  engines,  Code 

of  A.S.M.E.  for  1901  ....  487 

Tests  on  producer  plants,  table.  546 
Testing  of  gas  engines,  methods 

for ^186 

Testing  of  storage  batteries  ....  414 
Theoretical  and  actual  heat  en- 
engines,  comparison  of    .  61 

Theoretical  Brayton  cycle 69 

cycles,  comparison  of  73 

Diesel,  cycle    71 

Theoretical    Otto    cycle,    cyclic 

efficiency  of    68 

Theoretical    Otto    or    Beau    de 

Rochas  cycle    65 

Theoretical  yield  of  producer    .  .  153 

Theory  of  dissociation    98 

stratification    97 

Thermal  unit,  British 14 

Thermo  dynamics,  second    law 

of 55 

Thermo-element    8 

Thermometer,  air    8 

Thermometers,     :  .  .  6 

calorimetric    11 

electrical 8 

fusion    11 

vapor 11 

Thermometric  scales,  table  of  .  .  5 

Thermopyle 8 

Thompson  indicator   33 

Three-port  two-cycle  engine ....  366 

Three-terminal  spark  coil    405 

Throttling  engine,  Jacobson    .  .  .  272 

engines,  Warren  ....  295 

Time  of  explosion 227 

Timer,  Grouse-Hinds  double-ball  408 

Lacoste     407 

Pittsfield 407 

Sintz "...  406 

Timing  valve   395 

Timers  . 405 

Tod  gas  engine    306 

Total  operating  costs 568 

Transfer  of  heat  at  constant  pres- 
sure  .  50 


596 


INDEX 


PAGE 

Transfer    of    heat    at    constant 

volume    50 

Trembler  spark  coil    403 

True  explosive  mixture    215 

True    explosive     mixtures,     for 
commercial    gases,    table 

of 216 

Two-cycle  engine,   governing  of 

449,  467 

Koerting 313 

three-port 366 

Two-cycle  gas-engine,  Buckeye     286 
Two-cycle    marine   gasoline    en- 
gine, Lozier    364 

Two-cycle     oil     engine,     De  La 

Vergne    380 

Two-stroke  Otto  cycle 102 

Typical    computations    on    fuel 
mixtures     and     exhaust 

gases.  . 138 

Typical    diagram,    Otto-Langen 

free  piston  engine 248 

Typical  Diesel  engine  diagrams.    106 
Typical    lower    loop    diagrams, 

Otto  cycle 101 

Typical  Otto  cycle  diagrams  ...     94 


r 


Unit,  British  thermal 14 


Value  of  blast  furnace  gas 560 

Vapor  tension  for  alcohol  and 

water,  table  of 204 

Vapor  thermometers 11 

Vaporizer,  alcohol,  Diirr  201 

Vaporizer,  alcohol,  Swiderski- 

Longuemarre  199 

Vaporizer,  Altman  alcohol 198 

Vaporizer,  combination  alcohol 

and  gasoline 202 


PAGE 

Vaporizer,  Crossley 194 

crude  oil,  Economist 195 

Vaporizer,  crude  oil,  Fairbanks- 
Morse 389 

Vaporizer,  Deutz  alcohol 198 

Dresden  alcohol 201 

Gibbon  kerosene      193 

Priestman     194 

W.  Hay 190 

Vaporizing  devices  for  alcohol .  .    196 
Vaporizing  devices  for  crude  oil 

and  kerosene 192 

Variation    of   fuel    consumption 

with  load    554 

Variation  of  specific   heat  with 

temperature 220 

Velocity  of  flame  propagation.  .    227 
Vertical     gas    engine,  Westing- 
house  306 

Volume  of  scrubber  in   suction 

plants    176 

Volumetric  efficiencies  and  suc- 
tion pressures  for  Otto 
cycle,  table  of 86 


W 


Warren  hit-and-miss  engine    .  .  .  295 

throttling  engines 295 

Waste  and  oil,  cost  of    564 

Water  gas,  constants  for 212 

production  of 147 

Wiring,  low  tension  system  of  .  .  421 

Weights,  fly-wheel,  table  of.  ...  440 

Westinghouse  gas  engine 266 

Westinghouse  horizontal  gas  en- 
gine     304 

W^estinghouse     vertical     engine, 

governor  for 460 

Westinghouse  vertical  single-act- 
ing tandem  gas  engine   .  .  306 

Wet  and  dry  cells 410 

Wile  pressure  producer    160 

Wiring  employing  magnetos,  sys- 
tems of . .                              .  422 


INDEX 


597 


PAGE 

Wiring,  systems  of   420 

Work  performed  in  adiabatic  ex- 
pansion    53 

Work  performed  in  isothermal 

expansion 53 

Work,  rate  of 1 


PAGE 


Wright's  engine 235 


Yield  of  producer,  theoretical  . .    153 


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